Russia announced Thursday it could be forced to respond militarily if the United States does not meet its security demands, including that all American troops be pulled out of Eastern and Central Europe.
"In the absence of will on the American side to negotiate firm and legally binding guarantees on our security from the United States and its allies, Russia will be forced to respond, including with military-technical measures," the Russian Foreign Ministry said.
The statement is the latest in a back-and-forth between Russia and the West that started in December when Moscow put forward sweeping security demands to Washington and NATO.
The United States rejected key Russian demands, including a ban on Ukraine joining NATO and clauses limiting Western influence in Eastern Europe and former Soviet states.
In its formal follow-up Thursday, Russia also said it insists "on the withdrawal of all US armed forces in Central Europe, Eastern Europe and the Baltics."
It said the West should stop sending weapons to Ukraine, "withdraw Western advisers and instructors from there" and for NATO countries to refuse joint exercises with the Ukrainian army.
Thursday's statement comes as the United States and its allies say Russia has amassed more than 100,000 troops on the border with Ukraine and Moscow-annexed Crimea, raising concerns of a possible attack.
In the document, Russia denied it had plans to invade Ukraine, contradicting U.S. claims that an attack could come at any moment.
"There is no 'Russian invasion' of Ukraine, which the United States and its allies have been announcing officially since last fall, and it is not planned," the Foreign Ministry said.
U.S. President Joe Biden on Thursday said the threat of a Russian invasion was "very high," even though Moscow in recent days has announced several troop drawdowns from Ukraine and Crimea.
Washington and its allies have demanded that Russia pull back its troops from its neighbor's borders.
But in its document, Moscow lashed out at Western calls for Russia to move its soldiers and threats of a massive coordinated sanctions response.
"Ultimatums on withdrawing troops from certain areas of Russian territory, accompanied by threats of tougher sanctions are unacceptable and undermine the prospect of reaching a real agreement," it said.
It added that Russia's "red lines" and security interests "continue to be ignored."
Moscow this week announced that it was moving back some troops from Ukraine's border but Western leaders have said there is no evidence of a drawdown.