By YURAS KARMANAU and ADAM SCHRECK

KYIV, Ukraine (AP) — The besieged Ukrainian city of Mariupol yielded up more horrors after six weeks of pummeling by Russian troops, with the mayor saying more than 10,000 civilians have died in the strategic southern port, their corpses “carpeted through the streets.”

As Russia pounded targets around Ukraine and prepared for a major assault in the east, the country’s leader warned President Vladimir Putin’s forces could resort to chemical weapons, and Western officials said they were investigating an unconfirmed claim by a Ukrainian regiment that a poisonous substance was dropped in Mariupol.

The city has seen some of the heaviest attacks and civilian suffering in the war, but the land, sea and air assaults by Russian forces fighting to capture it have increasingly limited information about what’s happening inside the city.

Speaking by phone Monday with The Associated Press, Mariupol Mayor Vadym Boychenko accused Russian forces of having blocked weeks of attempted humanitarian convoys into the city in part to conceal the carnage. Boychenko said the death toll in Mariupol alone could surpass 20,000.

Boychenko also gave new details of allegations by Ukrainian officials that Russian forces have brought mobile cremation equipment to Mariupol to dispose of the corpses of victims of the siege. He said Russian forces have taken many bodies to a huge shopping center where there are storage facilities and refrigerators.

“Mobile crematoriums have arrived in the form of trucks: You open it, and there is a pipe inside and these bodies are burned,” the mayor said.

Boychenko spoke from Ukrainian-controlled territory outside Mariupol. The mayor said he had several sources for his description of the alleged methodical burning of bodies by Russian forces in the city, but did not detail the sources.

The discovery of large numbers of apparently massacred civilians after Russian forces retreated from cities and towns around the capital, Kyiv, already has prompted widespread condemnation and accusations that Russia is committing war crimes in Ukraine.

Those forces withdrew after they failed to take Kyiv in the face of stiff Ukrainian resistance, and Russia now says it will focus on the Donbas, an industrial region in Ukraine’s east. Already there are signs the military is gearing up for a major offensive there.

On a visit to Russia’s Far East on Tuesday, President Vladimir Putin insisted the military would achieve its goals in Ukraine, saying the campaign was aimed at ensuring Russia’s security and protecting civilians in the east. He added that his country had no intention of isolating itself and that foreign powers wouldn’t succeed in isolating it — despite a raft of sweeping economic sanctions.

Putin’s visit to the Vostochny space launch facility marked his first trip outside Moscow since Russia’s invasion on Feb. 24.

The British Defense Ministry said Russian forces are continuing to pull out of Belarus to support operations in eastern Ukraine, where it said fighting “will intensify over the next two to three weeks.”

While building up forces in the east, Russia continued to strike targets across Ukraine in a bid to wear down the country’s defenses. Russia’s defense ministry said Tuesday that it used used air- and sea-launched missiles to destroy an ammunition depot and airplane hangar at Starokostiantyniv in the western Khmelnytskyi region and an ammunition depot near Kyiv.

The Donbas has been torn by fighting between Russian-allied separatists and Ukrainian forces since 2014, and Russia has recognized the separatists’ claims of independence. Military strategists say Russian leaders appear to hope local support, logistics and terrain in the Donbas favor Russia’s larger and better-armed military, potentially allowing its troops to finally turn the tide decisively in their favor in a way they have struggled to thus far.

Russia has appointed a seasoned general to lead its renewed push in the Donbas, but questions remain about the ability of depleted and demoralized Russian forces to conquer much ground.

When their offensive in many parts of the country was thwarted, Russian forces increasingly relied on bombarding cities — a strategy that has flattened many urban areas and killed thousands of people. And Western officials have warned that Putin could resort to using unconventional weapons, particularly chemical agents — part of campaign by U.S. and U.K. authorities to release intelligence findings about Russian plans, in part as a deterrent.

Zelenskyy repeated the warning in his nightly address Monday, specifically saying the arms might be used in Mariupol. “We take this as seriously as possible,” Zelenskyy said.

A Russia-allied separatist official, Eduard Basurin, appeared to urge their use Monday, telling Russian state TV that separatist forces should seize a giant metals plant in Mariupol from Ukrainian forces by first blocking all the exits out of the factory. “And then we’ll use chemical troops to smoke them out of there,” he said.

A Ukrainian regiment defending the plant claimed Monday, without providing evidence, that a drone had dropped a poisonous substance on the city. It indicated there were no serious injuries.

The claim by the Azov Regiment, a far-right group now part of the Ukrainian military, could not be independently verified.

Basurin was quoted by the Interfax news agency as saying Tuesday that the separatist forces “haven’t used any chemical weapons in Mariupol.”

But Deputy Defense Minister Hanna Maliar said Ukrainian authorities were investigating. She told Ukrainian television that “there is a suggestion that likely it was, possibly, phosphorus munitions.” Britain has warned that Russia may use phosphorus bombs — which cause horrendous burns and whose use in civilian areas is banned under international law — in Mariupol.

Pentagon spokesman John Kirby said in a statement that the U.S. could not confirm the drone report out of Mariupol. But Kirby noted the administration’s persistent concerns “about Russia’s potential to use a variety of riot control agents, including tear gas mixed with chemical agents, in Ukraine.”

Foreign Secretary Liz Truss said the U.K. was “working urgently” to investigate the report.

Meanwhile, Western military analysts say Russia’s assault increasingly is focusing on an arc of territory stretching from Kharkiv, Ukraine’s second-largest city, in the north, to Kherson in the south.

A senior U.S. defense official on Monday described a long Russian convoy now rolling toward the eastern city of Izyum with artillery, aviation and infantry support, as part of redeployment for what appears to be the looming Russian campaign.

Ahead of that offensive, there seemed little diplomatic progress toward ending a war that has driven more than 10 million Ukrainians from their homes, more than 4 million of them from the country, left thousands dead.

The U.N. children’s agency said nearly two-thirds of all Ukrainian children have fled their homes since Russia’s invasion began, while Ukrainian authorities accuse Russian forces of committing atrocities, including a massacre in the town of Bucha, outside Kyiv, airstrikes on hospitals and a missile attack last week at a train station where people were trying to flee.

In Mariupol, meanwhile, about 120,000 civilians are in dire need of food, water, warmth and communications, the mayor said.

Ukraine accuses Russian forces of forcibly removing people from the city to Ukraine’s separatist-controlled east before sending them to distant, economically depressed areas in Russia. Russia has denied moving people against their will.

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Karmanau reported from Lviv, Ukraine. Associated Press writer Robert Burns in Washington, and AP journalists around the world contributed to this report.

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By ADAM SCHRECK and CARA ANNA

KYIV, Ukraine (AP) — Russia said Monday that it destroyed air defense systems in Ukraine over the weekend, in what appeared to be a renewed push to gain air superiority and take out weapons Kyiv has described as crucial ahead of a broad new offensive in the east.

Moscow’s initial invasion stalled on several fronts as it met with stiff resistance from Ukrainian forces, who prevented the Russians from taking the capital and other cities. The failure to win full control of Ukraine’s skies has hampered Moscow’s ability to provide air cover for troops on the ground, limiting their advances and likely exposing them to greater losses.

Russian Defense Ministry spokesman Maj. Gen. Igor Konashenkov said the military used cruise missiles to destroy four S-300 air defense missile launchers on the southern outskirts of the central city of Dnipro. He said about 25 Ukrainian troops were also hit by Sunday’s strike.

Konashenkov said Ukraine had received the air defense systems from a European country that he didn’t name. Last week, Slovakia said it handed over Soviet-designed S-300s to Ukraine — but Slovakia said it had no evidence that its system was hit.

With their advance in many parts of the country thwarted, Russian forces have relied increasingly on bombarding cities. The war has flattened many urban areas, killed thousands of people and left Russia politically and economically isolated. Ukrainian authorities accuse Russian forces of committing war crimes against civilians, including a massacre outside Kyiv, airstrikes on hospitals and a missile attack that killed at least 57 people at a train station.

Now, Russia is regrouping for a renewed push in the eastern Donbas region, where Moscow-backed separatists have been battling Ukrainian forces since 2014 and have declared independent states. Both sides are digging in for what could be a devastating war of attrition.

Russia has appointed a seasoned general to lead the effort, according to U.S. officials, though they do not see one man making a difference.

Ukrainian President Volodymyr Zelenskyy is meanwhile pleading for more Western aid, saying his forces need heavier firepower to resist the coming onslaught and push Russian forces back. Echoing his remarks in an AP interview, Zelenskyy said Sunday that the coming week could be crucial, with Western support to his country — or the lack thereof — proving decisive.

“To be honest, whether we will be able to (survive) depends on this,” Zelenskyy said in a “60 Minutes” interview. “Unfortunately, I don’t have the confidence that we will be receiving everything we need.”

Zelenskyy said he was grateful to U.S. President Joe Biden and other Western leaders for military aid to date but said he had “long ago” forwarded a list of specific items Ukraine desperately needs. In a video address to South Korean lawmakers on Monday, he specifically requested equipment that can shoot down Russian missiles.

Those armaments could increasingly come under attack as Russia looks to shift the balance in the 6-week-old war.

The Russian report of the attack on the S-300s outside Dnipro was the third such strike since the weekend. Konashenkov said the military also hit such systems in the Mykolaiv and Kharkiv regions. The Russian military claims couldn’t be independently verified.

Asked about the Russian claim that it had taken out systems supplied by a European country, Slovakian Foreign Minister Ivan Korcok said Monday he had “no evidence” that the Russians had destroyed the weaponry his country provided. Earlier, his government called reports that the Slovak-supplied system had been hit “disinformation.”

Ukraine already had a number of Soviet-built S-300s and other long-range air defense systems, and it also has received batches of portable, shoulder-fired Western anti-aircraft weapons like Stingers, which are efficient against low-flying aircraft.

Austrian Chancellor Karl Nehammer was due to meet Monday in Moscow with Russian President Vladimir Putin, after meeting with Zelenskyy in Kyiv. Austria, a member of the European Union, is militarily neutral and not a member of NATO.

Questions remain about the ability of depleted and demoralized Russian forces to conquer much ground after their advance on Kyiv was repelled by determined Ukrainian defenders.

Britain’s Defense Ministry said Monday that Ukraine has already beaten back several assaults by Russian forces in the eastern Donetsk and Luhansk regions — which make up the Donbas — resulting in the destruction of Russian tanks, vehicles and artillery.

In Washington, a senior U.S. official said Russia has appointed Gen. Alexander Dvornikov, one of its most experienced military chiefs, to oversee the invasion. The official was not authorized to be identified and spoke on condition of anonymity. Russia does not generally announce such appointments, and there was no comment from Moscow.

Dvornikov, 60, gained a reputation for brutality as head of Russian forces deployed to Syria in 2015 to back President Bashar Assad’s government during the country’s devastating civil war.

Until now, Russia has had no central war commander on the ground. But U.S. national security adviser Jake Sullivan, speaking Sunday on CNN’s “State of the Union,” played down the appointment’s significance.

“What we have learned in the first several weeks of this war is that Ukraine will never be subjected to Russia,” Sullivan said. “It doesn’t matter which general President Putin tries to appoint.”

Western military analysts say Russia’s assault increasingly is focusing on eastern Ukraine — an arc stretching from Kharkiv, Ukraine’s second-largest city, in the north, to Kherson in the south.

On Sunday, Russian forces shelled government-controlled Kharkiv and sent reinforcements toward Izyum to the southeast to try to break Ukraine’s defenses, the Ukrainian military said. The Russians also kept up their siege of Mariupol, a key southern port in the Donbas that has been besieged since nearly the start of the war.

Oleh Synyehubov, the regional governor of Kharkiv, said Monday that Russians shelling had killed 11 people over the last 24 hours, including a 7-year-old child.

The Institute for the Study of War, an American think tank, predicted that Russian forces will “renew offensive operations in the coming days” from Izyum in the campaign to conquer the Donbas, which comprises Ukraine’s industrial heartland.

But it said the outcome “remains very much in question.”

In Mariupol, Russia deployed Chechen fighters, reputed to be particularly fierce. Capturing the city on the Sea of Azov would give Russia a land bridge to the Crimean Peninsula, which Russia seized from Ukraine and annexed eight years ago.

In a video posted on his Telegram channel, Chechen Leader Ramzan Kadyrov said Russian forces would launch a renewed offensive on Mariupol as well as Kyiv and other cities. “Our offensive work will be not only in Mariupol, but in all the other settlements, cities and villages,” he said.

Mariupol’s residents have lacked food, water and electricity since Russian forces surrounded the city. Hundreds of thousands have fled, though Russian attacks have also frustrated evacuation missions.

Vladislav Usovich, an 18-year-old conscript serving in Russia-backed separatist forces, advanced slowly with other fighters through residential areas around a factory in Mariupol on Sunday.

“I thought it would go better, I thought it would be faster. Everything is going slowly,” he said. “The Ukrainians are prepared fighters. NATO trained them well.”

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This story has been updated to correct that the war began just over six weeks ago, not 10 weeks. ___

Anna reported from Bucha, Ukraine. Yesica Fisch in Borodyanko, Ukraine, Robert Burns and Calvin Woodward in Washington, and Associated Press journalists around the world contributed to this report.

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