Top Biden Aide Says Ukraine Invasion Could Come 'Any Day'

Meanwhile, elite U.S troops and equipment landed in southeastern Poland near the border with Ukraine.

White House national security adviser Jake Sullivan said Sunday that Russia could invade Ukraine "any day," launching a conflict that would come at an "enormous human cost."

The senior adviser to President Joe Biden offered another stark warning the day after U.S. officials confirmed that Russia has  assembled at least 70% of the military firepower it likely intends to have in place by mid-month to give President Vladimir Putin the option of launching a full-scale invasion of Ukraine.

"If war breaks out, it will come at an enormous human cost to Ukraine, but we believe that based on our preparations and our response, it will come at a strategic cost to Russia as well," Sullivan said.