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WASHINGTON (NEXSTAR) — As tensions at the Ukraine border continue to escalate, Western leaders are scrambling to broker a deal to prevent a Russian invasion that United States officials say could happen any day.

NATO leaders are working to present a united front opposing an invasion. President Joe Biden met with newly elected German Chancellor Olaf Scholz Monday to discuss the matter.

For weeks, Germany, a key U.S. ally, has been unenthusiastic about sending lethal military supplies to Ukraine or imposing sanctions on Russia. The reason: a newly constructed natural gas pipeline between Germany and Russia.

Despite the differences, Biden said the U.S. and Germany are “working in lockstep” and Scholz echoed that the two nations would “act together” if Russia won’t stand down. Biden said that if Russia invades Ukraine, the U.S. “will bring an end” to the pipeline.

The Pentagon says that more than 100,000 Russian troops have massed on the Ukraine border.

“Which each passing day, he (Russian President Vladimir Putin) gives himself a lot of more options from a military perspective,” Pentagon spokesman John Kirby said.

“This is not alarmism. This is simply the facts,” U.S. Secretary of State Antony Blinken said at a Monday joint press conference with a top European Union official.

He and EU High Representative for Foreigh Affairs Josep Borrell said it’s up to Russia to deescalate.

“Certainly we are living … in the most dangerous moment for the security in Europe after the end of the Cold War,” Borrell said. “But at the same time, we believe that there is still room for diplomacy.”

So far, negotiations with Russia have made little progress, with Russian President Vladimir Putin demanding limits on Ukraine’s future that NATO allies refuse to accept. And the window for diplomacy is appearing to narrow.

Biden warned any American civilians in Ukraine to leave.