President Joe Biden met with Germany's new leader on Monday in a flurry of diplomacy across two continents, vowing to block the crucial Nord Stream 2 Russia-to-Germany gas pipeline if "Russia invades Ukraine."

However, Russian President Vladimir Putin retorted that the US and its allies are the only ones talking about an invasion.

Putin and French President Emmanuel Macron met in Moscow for more than five hours at the same time as Biden and German Chancellor Olaf Scholz spoke at the White House in an attempt to defuse the crisis before it escalates into an armed conflict.

US sanctions if 'Russia invades'

The White House has grown increasingly concerned about the possibility of war, and Biden has been trying to rally support among European allies for crippling economic sanctions against Russia if it attacks.

“If Russia invades, that means tanks and troops crossing the border of Ukraine again, then there will no longer be a Nord Stream 2,” Biden said. “We will bring an end to it.”

That would intend to hurt Russia economically but also cause supply problems for Germany. Construction of the pipeline has been completed, but it is not yet operating.

“We are jointly ready, and all of NATO is ready,” Biden said, referring to the powerful Western alliance, though Ukraine is not a member.

While Biden was adamant that the pipeline would not be built, Scholz emphasized the importance of maintaining some ambiguity about sanctions to pressure Russia to de-escalate the crisis.

“It’s necessary for Russia to understand that a lot more could happen than they’ve perhaps calculated with themselves,” Scholz said.

Moscow's demands ignored

Russia could invade Ukraine "any day", according to White House National Security Advisor Jake Sullivan, triggering a conflict with "enormous human cost."

At the same time, Biden and NATO allies have stated unequivocally that no troops will be sent in to fight Russia on Ukraine's behalf.

During their lengthy meeting, Macron and Putin expressed their disagreements while also emphasizing the need for more talks.

Putin stated that the US and NATO have ignored Moscow's demands that the alliance guarantee that Ukraine and other ex-Soviet countries will be kept out, that weapons will not be placed in Ukraine, and that alliance forces will be withdrawn from Eastern Europe.

Putin signaled his readiness to continue negotiations and denied anew that Russia has any intention of invading Ukraine.

Foreign troops deploy

In the meantime, Biden warned “it would be wise” for Americans other than essential diplomats to leave Ukraine.

On a more positive note, Putin stated flatly that some of Macron's proposals could serve as a basis for resolving the conflict in eastern Ukraine, and they agreed to speak after Macron's visit to Kiev on Tuesday.

"The answer is yes," Biden said when asked if there was still an "offramp" for Russia in the standoff.

Additional US troops have already been deployed to Poland, Romania, and Germany, and a few dozen US troops and equipment arrived in southeastern Poland near the Ukraine border on Sunday, with hundreds more infantry troops from the 82nd Airborne Division expected to arrive soon.

Britain said the UK was sending 350 troops to Poland to bolster NATO forces, joining 100 Royal Engineers already there.