Russia on Monday summoned the US ambassador in protest after President Joe Biden branded Russian leader Vladimir Putin a “war criminal” for Moscow’s actions in Ukraine, saying he had endangered ties.

“Such statements by the American president, which are not worthy of a high-ranking statesman, have put Russian-American relations on the verge of rupture,” the foreign ministry said in a statement.

The statement said ambassador John Sullivan had been handed a formal letter of protest over “recent unacceptable statements” made by Biden.

He was warned that “hostile actions taken against Russia would receive a firm and decisive response,” the ministry said.

Biden described Putin as a “war criminal” in remarks to reporters last week, amid heavy fighting in Ukraine after Moscow sent tens of thousands of troops into the pro-Western country.