By NEBI QENA and CARA ANNA

KYIV, Ukraine (AP) — Ukrainian forces said they retook a strategically important suburb of Kyiv early Tuesday, as Russian forces squeezed other areas near the capital and their attack on the embattled southern port of Mariupol raged unabated.

Explosions and bursts of gunfire shook Kyiv, and black smoke rose from a spot in the north. Intensified artillery fire could be heard from the northwest, where Russia has sought to encircle and capture several suburban areas of the capital, a crucial target.

Residents sheltered at home or underground under a 35-hour curfew imposed by city authorities that runs to Wednesday morning.

Russian forces also carried on with their siege of Mariupol after the southern port city’s defenders refused demands to surrender, with fleeing civilians describing relentless bombardments and corpses lying in the streets. But the Kremlin’s ground offensive in other parts of the country advanced slowly or not at all, knocked back by lethal hit-and-run attacks by the Ukrainians.

Early Tuesday, Ukrainian troops forced Russian forces out of the Kyiv suburb of Makariv after a fierce battle, Ukraine’s Defense Ministry said. The regained territory allowed Ukrainian forces to retake control of a key highway and block Russian troops from surrounding Kyiv from the northwest.

Still, the Defense Ministry said Russian forces battling toward Kyiv were able to partially take other northwest suburbs, Bucha, Hostomel and Irpin, some of which had been under attack almost since Russia’s military invaded almost a month ago.

Russian President Vladimir Putin’s forces are increasingly concentrating their air power and artillery on Ukraine’s cities and the civilians living there. Moscow’s invasion has driven nearly 3.5 million people from Ukraine, according to the United Nations, with another 6.5 million displaced inside the country. The U.N. has confirmed over 900 civilian deaths while saying the real toll is probably much higher. Estimates of Russian deaths vary, but even conservative figures are in the low thousands.

U.S. and British officials say Kyiv remains Russia’s primary objective. The bulk of Moscow’s forces remain miles from the center, but missiles and artillery have destroyed apartment buildings and a large shopping mall, which was left a smoking ruin after being hit late Sunday by strikes that killed eight people, according to emergency officials.

A senior U.S. defense official, speaking on condition of anonymity to discuss the military’s assessment, said Russia had increased air sorties over the past two days, carrying out as many as 300 in the past 24 hours, and has fired more than 1,100 missiles into Ukraine since the invasion began.

U.S. President Joe Biden, who is heading to Europe later in the week to meet with allies, suggested Monday evening that worse may be still to come.

“Putin’s back is against the wall,” Biden said. “He wasn’t anticipating the extent or the strength of our unity. And the more his back is against the wall, the greater the severity of the tactics he may employ.”

Biden reiterated accusations that Putin is considering resorting to using chemical weapons.

As Russian forces try to squeeze Kyiv, talks to end the fighting have continued by video but failed to bridge the chasm between the two sides. Ukrainian President Volodymyr Zelenskyy told Ukrainian television late Monday that he would be prepared to consider waiving any NATO bid by Ukraine — a key Russian demand — in exchange for a cease-fire, the withdrawal of Russian troops and a guarantee of Ukraine’s security.

Zelenskyy also suggested Kyiv would be open to future discussions on the status of Crimea, which Russia seized in 2014, and the regions of the eastern Donbas region held by Russian-backed separatists. But he said that was a topic for another time. Zelenskyy plans to speak to Italy’s lawmakers Tuesday and Japanese lawmakers on Wednesday, part of a series of addresses to foreign legislatures as he seeks to drum up support.

In Mariupol, with communications crippled, movement restricted and many residents in hiding, the fate of those inside an art school flattened on Sunday and a theater that was blown apart four days earlier was unclear. More than 1,300 people were believed to be sheltering in the theater, and 400 were estimated to have been in the art school.

Perched on the Sea of Azov, Mariupol is crucial port for Ukraine and lies along a stretch of territory between Russia and Crimea. As such, it is a key target that has been besieged for more than three weeks and has seen some of the worst suffering of the war.

It is not clear how close its capture might be. Ukraine’s Defense Ministry said Tuesday that their forces were still defending the city and had destroyed a Russian patrol boat and electronic warfare complex.

Over the weekend, Moscow had offered safe passage out of Mariupol — one corridor leading east to Russia, another going west to other parts of Ukraine — in return for the city’s surrender before daybreak Monday. Ukraine flatly rejected the offer well before the deadline.

Mariupol had a prewar population of about 430,000. Around a quarter were believed to have left in the opening days of the war, and tens of thousands escaped over the past week by way of the humanitarian corridors. Other attempts have been thwarted by the fighting.

Mariupol officials said on March 15 that at least 2,300 people had died in the siege, with some buried in mass graves. There has been no official estimate since then, but the number is feared to be far higher after six more days of bombardment.

For those who remain, conditions have become brutal. The assault has cut off Mariupol’s electricity, water and food supplies and severed communication with the outside world, plunging residents into a fight for survival. Fresh commercial satellite images showed smoke rising from buildings newly hit by Russian artillery.

Those who have made it out of Mariupol told of a devastated city.

“There are no buildings there anymore,” said 77-year-old Maria Fiodorova, who crossed the border to Poland on Monday after five days of travel.

Olga Nikitina, who fled Mariupol for the western Ukrainian city of Lviv, where she arrived Sunday, said gunfire blew out her windows, and her apartment dropped below freezing.

“Battles took place over every street. Every house became a target,” she said.

A long line of vehicles stood on a road in Bezimenne, east of Mariupol, as residents of the besieged city sought shelter at a temporary camp set up by Russian-backed separatists in the Donetsk region. An estimated 5,000 people from Mariupol have taken refuge in the camp. Many arrived in cars with signs that said “children” in Russian.

A woman who gave her name as Yulia said she and her family sought shelter in Bezimenne after a bombing destroyed six houses behind her home.

“That’s why we got in the car, at our own risk, and left in 15 minutes because everything is destroyed there, dead bodies are lying around,” she said. “They don’t let us pass through everywhere — there are shootings.”

In all, more than 8,000 people escaped to safer areas Monday through humanitarian corridors, including about 3,000 from Mariupol, Deputy Prime Minister Iryna Vereshchuk said.

Russian shelling of a corridor wounded four children on a route leading out of Mariupol, Zelenskyy said.

Matthew Saltmarsh, a spokesman for the U.N. refugee agency called the speed and scale of people fleeing danger in Ukraine “unprecedented in recent memory.”

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This story has been updated to correct that Zelenskyy plans to address Japanese lawmakers on Wednesday, not Tuesday.

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Anna reported from Lviv, Ukraine. Associated Press writer Yuras Karmanau in Lviv, and other AP journalists around the world contributed to this report.

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Follow the AP’s coverage of the war at https://apnews.com/hub/russia-ukraine

By CARA ANNA

LVIV, Ukraine (AP) — Ukrainian officials defiantly rejected a Russian demand that their forces in Mariupol lay down arms and raise white flags Monday in exchange for safe passage out of the besieged strategic port city.

Even as Russia intensified its attempt to pummel Mariupol into surrender, its offensive in other parts of Ukraine has floundered. Western governments and analysts say the broader conflict is grinding into a war of attrition, with Russia continuing to bombard cities.

In the capital, Kyiv, a shopping center in the densely populated Podil district near the city center was a smoldering, flattened ruin after being hit late Sunday by shelling that killed eight people, according to emergency officials. The force of the explosion shattered every window in a neighboring high-rise. Artillery boomed in the distance as firefighters picked their way through the destruction.

Ukrainian authorities also said Russia shelled a chemical plant in northeastern Ukraine, sending toxic ammonia leaking into the air, and hit a military training base in the west with cruise missiles.

The encircled southern city of Mariupol on the Sea of Azov has seen some of the worst horrors of the war, under Russian pounding for more than three weeks, in a brutal assault that Ukrainian and Western officials have called a war crime.

Strikes hit an art school sheltering some 400 people only hours before Russia’s offer to open corridors out of the city in return for the capitulation of its defenders, according to Ukrainian officials.

“They are under the rubble, and we don’t know how many of them have survived,” Ukraine’s President Volodymyr Zelenskyy said. In a video address, he vowed that Ukraine would “shoot down the pilot who dropped that bomb.”

Russian Col. Gen. Mikhail Mizintsev had offered two corridors — one heading east toward Russia and the other west to other parts of Ukraine — in return for Mariupol’s surrender. He did not say what Russia planned if the offer was rejected.

The Russian Ministry of Defense said authorities in Mariupol could face a military tribunal if they sided with what it described as “bandits,” the Russian state news agency RIA Novosti reported.

Ukrainian officials rejected the proposal even before Russia’s deadline of 5 a.m. Moscow time (0200GMT) for a response came and went.

“There can be no talk of any surrender, laying down of arms,” Ukrainian Deputy Prime Minister Irina Vereshchuk told the news outlet Ukrainian Pravda. “We have already informed the Russian side about this.”

Mariupol Mayor Piotr Andryushchenko also quickly dismissed the offer, saying in a Facebook post he didn’t need to wait until the morning deadline to respond and cursing at the Russians, according to the news agency Interfax Ukraine.

The strike on the art school was the second time in less than a week that officials reported an attack on a public building where Mariupol residents had taken shelter. On Wednesday, a bomb hit a theater where more than 1,000 people were believed to be sheltering. At least 130 people were reported rescued Friday, but there has been no update since then.

Mariupol officials said at least 2,300 people have died in the siege, with some buried in mass graves.

City officials and aid groups say Russian bombardment has cut off Mariupol’s electricity, water and food supplies and severed its communications with the outside world, plunging the remaining residents into a chaotic fight for survival.

“What’s happening in Mariupol is a massive war crime,” EU foreign policy chief Josep Borrell said Monday.

Russia’s invasion has rocked the international security order and driven nearly 3.4 million people from Ukraine, according to the United Nations. The U.N. has confirmed 902 civilian deaths in the war but concedes the actual toll is likely much higher. Estimates of Russian deaths vary, but even conservative figures are in the low thousands.

Multiple attempts to evacuate residents from Mariupol and other Ukrainian cities have failed or only partly succeeded, with bombardments continuing as civilians tried to flee.

Some who were able to escape Mariupol tearfully hugged relatives as they arrived by train Sunday in Lviv in western Ukraine.

“Battles took place over every street. Every house became a target,” said Olga Nikitina, who was embraced by her brother as she got off the train. “Gunfire blew out the windows. The apartment was below freezing.”

Mariupol is a key Russian target because its fall would allow Russian forces in southern and eastern Ukraine to unite. But Western military analysts say that even if the city is taken, the troops battling a block at a time for control there may be too depleted to help secure Russian breakthroughs on other fronts.

More than three weeks into the invasion, the two sides now seem to be trying to wear each other down, experts say, with bogged-down Russian forces launching long-range missiles at cities and military bases as Ukrainian forces carry out hit-and-run attacks and seek to sever Russian supply lines.

U.S. Defense Secretary Lloyd Austin said Ukrainian resistance means Russian President Vladimir Putin’s “forces on the ground are essentially stalled.”

Talks between Russia and Ukraine have continued by video conference but failed to bridge the chasm between the two sides, with Russia demanding Ukraine disarm and Ukraine saying Russian forces must withdraw from the whole country.

Zelenskyy has said he would be prepared to meet Putin in person, but Kremlin spokesman Dmitry Peskov said Monday that more progress must be made first. He said that “so far significant movement has not been achieved” in the talks.

U.S. President Joe Biden was expected to talk later Monday with the leaders of France, Germany, Italy and Britain to discuss the war, before heading later in the week to NATO and Group of Seven summits in Brussels and then Poland.

In Ukraine’s major cities, hundreds of men, women and children have been killed in Russian attacks.

Ukraine’s prosecutor general said a Russian shell struck a chemical plant outside the eastern city of Sumy just after 3 a.m. Monday, causing a leak in a 50-ton tank of ammonia that took hours to contain.

Russian military spokesman Igor Konashenkov claimed the leak was a “planned provocation” by Ukrainian forces to falsely accuse Russia of a chemical attack.

Konashenkov also said an overnight cruise missile strike hit a military training center in the Rivne region of western Ukraine. He said 80 foreign and Ukrainian troops were killed, though the figure could not be independently confirmed. Vitaliy Koval, the head of the Rivne regional military administration, confirmed a twin Russian missile strike on a training center there early Monday but offered no details about injuries or deaths.

Britain’s defense ministry said Monday that Ukrainian resistance had kept the bulk of Russian forces more than 25 kilometers (15 miles) from the city center, but that Kyiv “remains Russia’s primary military objective.”

Russian troops are shelling Kyiv for a fourth week now and are trying to surround the capital, which had nearly 3 million people before the war. Kyiv Mayor Vitali Klitschko announced a curfew in the capital from Monday evening to 7 a.m. local time Wednesday, telling residents to stay at home or in shelters.

A cluster of villages on Kyiv’s northwest edge, including Irpin and Bucha, have been all but cut off by Russian forces and are on the verge of humanitarian catastrophe, regional officials said. Associated Press journalists who were in the area a week ago saw bodies in a public park, and not a day goes by without smoke rising from the area.

In another worrying development, Ukraine’s nuclear regulatory agency said radiation monitors around the Chernobyl nuclear power plant, site of the world’s worst meltdown in 1986, have stopped working.

The agency said that, and a lack of firefighters to protect the area’s radiation-tainted forests as the weather warms, could mean a “significant deterioration” in the ability to control the spread of radiation in Ukraine and beyond.

Concerns have been expressed for safety at the shuttered plant since it was seized by Russian forces on Feb. 24, the first day of the invasion. Management at the plant said Sunday that 50 staff members who had been working nonstop since the Russian takeover have been rotated out and replaced.

Earlier this month Russia shelled the working Zaporizhzhia nuclear plant, though no radiation was released.

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Associated Press writer Yuras Karmanau in Lviv, Ukraine, and other AP journalists around the world contributed to this report.

Follow the AP’s coverage of the war at https://apnews.com/hub/russia-ukraine