KYIV, April 11 - The mayor of the Ukrainian port city of Mariupol said Monday that more than 10,000 civilians have died in the Russian siege of his city, and that the death toll could surpass 20,000, as weeks of attacks and privation leave the bodies of Mariupol’s people “carpeted through the streets.”

Speaking by phone Monday with The Associated Press, Mayor Vadym Boychenko also accused Russian forces of having blocked weeks of thwarted humanitarian convoys into the city in an attempt to conceal the carnage there from the outside world.

Mariupol has been cut off by Russian attacks that began soon after Russian President Vladimir Putin launched the invasion of Ukraine in late February, and has suffered some of the most brutal assaults of the war. Boychenko gave new details of recent allegations by Ukrainian officials that Russian forces have brought mobile cremation equipment to Mariupol to dispose of the corpses of victims of the siege.

Russian forces have taken many bodies to a huge shopping center where there are storage facilities and refrigerators, Boychenko said.

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

Boychenko spoke from a location in Ukrainian-controlled territory but outside Mariupol. The mayor said he had several sources for his description of the allegedly methodic burning of corpses by Russian forces in the city, but did not detail the sources of his information.

The discovery of large numbers of apparently executed civilians after Russian forces retreated from cities around the capital, Kyiv, this month already has prompted widespread condemnation and charges from Ukrainians and the West that Russia is committing war crimes in Ukraine.

President Volodymyr Zelenskyy warned Ukrainians on Monday that Russia might use chemical weapons in Mariupol. “We take this as seriously as possible,” Zelenskyy said in his nightly address.

Western leaders have warned since before Russian troops moved into Ukraine that Russia could resort to unconventional weapons there, particularly chemical agents.

A Russia-allied separatist official, Eduard Basurin, appeared to urge their use Monday, telling Russian state TV that Russian-backed 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, without evidence, claimed Monday that a drone had dropped a poisonous substance in Mariupol but said there were no serious injuries.

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.”

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

Only those residents who have passed the Russian “filtration camps” are released from the city, Boychenko said.

Ukrainian officials say Russian troops are confiscating passports from Ukrainian citizens then moving them to “filtration camps” in Ukraine’s separatist-controlled east before sending them to distant, economically depressed areas in Russia.

Boychenko said that improvised prisons were organized for those who did not pass the “filtering,” while at least 33,000 people were taken to Russia or to separatist territory in Ukraine. (ap/ez)