U.S. President Joe Biden on Thursday strengthened his warning to Russia about a potential attack on Ukraine, saying that any movement of Russian units across the Ukrainian border would be taken as an invasion, a day after the president triggered alarm in European capitals with his suggestion of divisions among allies.

Biden, speaking to reporters at the White House after hours of efforts by his administration to walk back his comments in a news conference Wednesday, insisted that he had been "absolutely clear” with President Vladimir Putin of Russia that a new incursion in Ukraine would be met by a "severe and coordinated economic response.”

Biden retraced his rhetorical steps as Secretary of State Antony Blinken met with U.S. allies in Germany before a critical Friday sit-down in Geneva with Foreign Minister Sergey Lavrov of Russia, after several rounds of inconclusive discussions over the huge buildup of Russian troops along Ukraine’s eastern border.