US President Joe Biden will speak with European leaders as Washington intensifies its diplomatic efforts in the face of what it calls an increasingly likely Russian invasion of Ukraine.

Biden will host a call with the leaders of Canada, France, Germany, Italy, Poland, Romania, Britain, the European Union and NATO later on Friday, the White House said.

The Biden administration has said that a diplomatic solution remains possible if Russia chooses but that Washington and its European allies are prepared to enact harsh punishments if Moscow opts to invade. Biden on Thursday said a Russian invasion could come in the next few days.

The call comes as the US ambassador to the Organization for Security and Cooperation in Europe said Russia’s buildup of military personnel threatening Ukraine probably totals up to 190,000.

Meanwhile, US Vice President Kamala Harris met NATO Secretary-General Jens Stoltenberg at the Munich Security Conference on Friday, expressing concern amid the build-up and vowing to stay in close contact with NATO and US allies.

“We feel very strongly about and will always be committed to the principle of territorial integrity and sovereignty,” Harris told reporters. “We remain of course supportive of diplomacy as it relates to the dialogue and discussions we’ve had with Russia, but we are also committed to taking corrective actions.”

US Secretary of State Antony Blinken will also address the conference on Friday, one day after his unexpected address to the United Nations Security Council in which he warned that Russia was planning an attack on neighboring Ukraine within days.

Blinken also agreed to meet Russian Foreign Minister Sergei Lavrov next week as long as Russia has not invaded first.

US Defense Secretary Lloyd Austin also spoke with his Russian counterpart on Friday, the Pentagon said in a statement.