US assures Ukraine of 'swift and decisive' response to any further Russian aggression

US President Joe Biden assured his Ukrainian counterpart Sunday that the US would "respond swiftly and decisively" to any further Russian aggression against his country.

In a phone call with Volodymyr Zelensky, Biden "reaffirmed the commitment of the United States to Ukraine's sovereignty and territorial integrity," said a White House readout of the conversation.

The American president also "made clear that the United States would respond swiftly and decisively, together with its Allies and partners, to any further Russian aggression against Ukraine."

Biden and Zelensky "agreed on the importance of continuing to pursue diplomacy and deterrence in response to Russia's military buildup on Ukraine's borders," it added.

For its part, the Ukrainian presidency in a statement said the two leaders addressed "the security situation around our country - exchanged available information, its assessments and discussed ways of de-escalation."

Zelensky stressed that "the Ukrainian party understands all current risks and is ready for any developments," according to the statement.

"We will stop any escalation towards Ukraine. The capital of Ukraine, Kyiv, and other cities of our state -- Kharkiv and Lviv, Dnipro and Odesa -- are safe and under reliable protection," he noted.

Zelensky thanked Biden for America's "unwavering support" and also invited him to visit Ukraine.

"I am convinced that your arrival in Kyiv in the coming days, which are crucial for stabilizing the situation, will be a powerful signal and contribute to de-escalation," he said.

The US has previously made clear that its response to an invasion of Ukraine would not be a military engagement with Russia but rather punishing sanctions.

The US on Friday warned that Russia could invade Ukraine "at any time," even amid frenzied diplomatic efforts to avoid war.

Ukraine has been plagued by conflict in its eastern regions since March 2014, following Russia's invasion and annexation of Crimea.

Moscow recently amassed more than 100,000 troops near Ukraine, prompting fears that the Kremlin could be planning another military offensive against its former Soviet neighbor.

Russia has denied that it is preparing to invade and accused Western countries of undermining its security through NATO's expansion towards its borders.

The Kremlin also issued a list of security demands to the West, including a rollback of troop deployments from some ex-Soviet states and guarantees that Ukraine and Georgia would not join NATO.