Russia has denounced the United States' claims that Moscow was committing crimes against humanity in Ukraine.

Washington is trying to demonize Moscow and foment the crisis in Ukraine with allegations of Russian crimes against humanity, Russia's ambassador to the United States said Sunday.

The Biden administration formally concluded that Russia has committed "crimes against humanity" during its nearly yearlong invasion of Ukraine, Vice President Kamala Harris said Saturday.

"We regard such insinuations as an unprecedented attempt to demonize Russia in the framework of the hybrid war unleashed against us," Ambassador Anatoly Antonov said in a statement on the Russian Embassy's Telegram messaging platform.

"There is no doubt that the purpose of such attacks by Washington is to justify its own actions to fuel the Ukrainian crisis."

Organizations supported by the U.S. Agency for International Development have documented more than 30,000 war crime incidents since the invasion, according to the U.S. government.

Ukrainian officials said they were investigating the Thursday shelling of the city of Bakhmut as a possible war crime.

The U.N.-backed Commission of Inquiry on Ukraine says it has identified war crimes but has not concluded whether they amount to crimes against humanity.

Friday will mark a year since Russia launched what it calls "a special military operation" to "denazify" and "demilitarise" its neighbor.

Ukraine's President Volodymyr Zelenskyy and Kyiv's Western allies call the invasion, which has no end in sight, an unprovoked, imperialistic land grab.

The war has killed tens of thousands, uprooted millions, pummelled the global economy and made Russian President Vladimir Putin a pariah in the West.

The Kremlin has intensified operations across a broad swath of southern and eastern Ukraine, and a major new offensive has been widely anticipated.

The United States and its allies have provided Ukraine with increasingly sophisticated arms, including modern battle tanks, and Western leaders have discussed more aid at a series of meetings in Europe in recent days.