Russia-Ukraine updates: US to ban Russian carriers from its airspace

Vice President Kamala Harris this week will make one of her most significant foreign policy trips since taking office, heading to Germany to lead the U.S. delegation at the Munich Security Conference -- where she will meet with Ukrainian President Volodymyr Zelenskyy.

"We are in a very decisive moment," a senior administration official told reporters as Harris prepared to lead the U.S. delegation, calling it a "resounding signal that engagement with our allies and partners is an absolutely critical part of our overall diplomacy in our approach to this situation."

During the Wednesday night call, senior administration officials said the tensions with Russia will be a major focus of the vice president's time abroad, with her schedule featuring a "series of high-stakes, high-level diplomatic talks."

Harris' most notable meeting will be with the Ukrainian president on Saturday.

"That'll be a real opportunity to underscore our commitment to Ukraine sovereignty and territorial integrity and to further coordinate the diplomatic efforts that have been underway to provide economic, and defensive security in Ukraine," an official said.

Harris is also expected to meet with NATO Secretary General Jens Stoltenberg, German Chancellor Olaf Scholz, and the leaders of Latvia, Lithuania and Estonia.

She will deliver keynote remarks at the conference, where she is expected to address the situation on Ukraine's borders -- touching on diplomatic, military and economic coordination of allies. 

"The vice president will underscore how that unity is a source of strength that will allow us to respond quickly and severely to any further Russian aggression," an official said.

-ABC News' Molly Nagle

Russia has increased its presence along the Ukrainian border by as many as 7,000 troops in the last few days, with some arriving Wednesday, a senior White House official told ABC News.

The assessment comes a day after the Russian government said it has started to withdraw some troops from near Ukraine's borders.

The official didn't comment on the total number of Russian forces currently along the border. 

President Joe Biden said Tuesday that Russia has "more than 150,000 troops encircling Ukraine and Belarus and along Ukraine's border." It's unclear if that number includes any of the new troops cited by the official.

Private satellite imaging company Maxar on Wednesday released over two dozen new images from the last 48 hours that continue to show Russia's heightened military activity in Belarus, Crimea and western Russia.

They include images that show a new 20-strong attack helicopter unit deployed in Belarus, a field hospital in Belarus and a pontoon bridge that has appeared across a river in Belarus, four miles from Ukraine’s border.

At least three of the images indicate some troops have departed or are preparing to depart, according to Maxar, though it's unclear where the troops are going.

-ABC News' Mary Bruce and Patrick Reevell

President Joe Biden had a secure call Wednesday afternoon with German Chancellor Scholz, according to the White House, ahead of Secretary of State Antony Blinken traveling to Germany on Thursday for the Munich Security Conference.

The two leaders "reaffirmed their commitment to Ukraine’s sovereignty and territorial integrity" and "underscored the importance of continued transatlantic coordination on diplomacy and deterrence measures," the White House said.

Scholz visited the Kremlin and met with Russian President Vladimir Putin on Wednesday, after meeting with Ukrainian President Volodymyr Zelenskyy in Kyiv on Monday. The German chancellor has said that war is "unimaginable" and shouldn't be an option since Ukraine has not formally requested to join NATO, as Russia demands it be barred from doing so.

"That is why it is somewhat peculiar to observe that the Russian government is making something that is practically not on the agenda the subject of major political problems," Scholz said earlier this week.

"That is, after all, the challenge we are actually facing. That something that is not at all an issue now is being made an issue," he said.

British Army Lt. Gen. James Hockenhull, chief of defense intelligence, said Wednesday that the U.K. has also not seen evidence that Russia is withdrawing substantial forces from near Ukraine, matching comments from NATO and U.S. officials.

"We have not seen evidence that Russia has withdrawn forces from Ukraine’s borders. Contrary to their claims, Russia continues to build up military capabilities near Ukraine," Hockenhull said in a rare public statement. 

"This includes sightings of additional armoured vehicles, helicopters and a field hospital moving towards Ukraine’s borders. Russia has the military mass in place to conduct an invasion of Ukraine," he said.

Russian units that are supposedly pulling back appear to actually be returning to their home bases that are already located next to Ukraine. Security analysts say that Russia appears to simply be shuffling its forces for the time being, while more continue to arrive.

France's Foreign Minister Jean Yves Le Drian in the French Senate Wednesday also said, for now, they are unable to say whether Russian troops are withdrawing or rotating but that Russia has all the elements in place for an attack.

-ABC News' Matt Seyler, Patrick Reevell and Anna Rabe