U.S. President Joe Biden and his Russian counterpart Vladimir Putin failed to make a breakthrough in their talks on Saturday that took place amid heightened concerns over a possibly imminent Russian invasion of Ukraine, according to a U.S. government official.

"There was no fundamental change in the dynamic that has been unfolding now for several weeks," the official said following the phone call between the two leaders, referring to the tension over Russia's military buildup on the borders of Ukraine.

Combined photo shows U.S. President Joe Biden (L) and Russian President Vladimir Putin. (Getty/Kyodo)

The call took place after the U.S. national security adviser, Jake Sullivan, warned on Friday that a possible Russian invasion of Ukraine could begin "any day now," including during the Beijing Winter Olympics taking place through Feb. 20.

During the one-hour call, Biden made clear to Putin that any aggression will result in "swift and severe costs on Russia," the White House said in press release. Washington is preparing to impose severe economic sanctions in coordination with its allies should Russia goes ahead with military actions.

Biden also said a further Russian invasion of Ukraine, which would follow its annexation of Crimea in 2014, would "produce widespread human suffering and diminish Russia's standing," according to the White House.

"President Biden was clear with President Putin that while the United States remains prepared to engage in diplomacy, in full coordination with our allies and partners, we are equally prepared for other scenarios," it added.

The official who briefed reporters about the call said, "It remains unclear whether Russia is interested in pursuing its goals diplomatically as opposed to through the use of force."

U.S. soldiers arrive in Mihail Kogalniceanu military base in Romania on Feb. 11, 2022. (Anadolu Agency/Getty/Kyodo)

As tension ticks up, the State Department said Saturday it has ordered the departure of most of the remaining staff in the U.S. Embassy in Ukraine.

It also urged in a travel advisory that American citizens depart "immediately" via commercial or private means. Routine consular services at the embassy in Kiev will be suspended, although emergency services will be provided in Lviv in western Ukraine.

A senior State Department official stressed it is "not just time to leave Ukraine, it is past time for private citizens to leave Ukraine."

Sullivan said Friday that Russia has "all the forces it needs to conduct a major military action," which could take a variety of forms, including "very real possibilities that it will involve the seizure of a significant amount of territory in Ukraine and the seizure of major cities including the capital city."

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