Russia warned on Monday that relations with the U.S. are on the brink of collapse and summoned the U.S. ambassador for an official protest against President Joe Biden’s remarks about Russian President Vladimir Putin.

A Russian Foreign Ministry statement referred to "recent unacceptable statements" by Biden about Putin.

Biden referred to Putin last week as a "war criminal" for sending tens of thousands of troops to invade Ukraine.

The Foreign Ministry said that at the meeting with U.S. Ambassador to Moscow John Sullivan "it was emphasized that remarks such as these by the American President, which are unworthy of a state figure of such a high rank, put Russian-American relations on the verge of a breach."

The Kremlin earlier described the comments as "personal insults" against Putin.

The ministry also told Sullivan that hostile actions against Russia would receive a "decisive and firm response."

Russia sent tens of thousands of troops into Ukraine on Feb. 24 in what it called a "special operation" to degrade its southern neighbor’s military capabilities and root out people it called dangerous nationalists.

Ukrainian forces have mounted stiff resistance against Russian forces and the West has imposed sweeping sanctions on Moscow in an effort to force it to withdraw.