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

Russia has expelled the second-most senior U.S. official at the American embassy in Moscow, a spokesperson for the U.S. Department of State said Thursday.

U.S. Deputy Chief of Mission Bart Gorman had not completed his tour and still had a valid Russian visa, according to the spokesperson, but Russia has ordered him to leave the country. The decision was "unprovoked, and we consider this an escalatory step and are considering our response," the spokesperson told ABC News.

The United States and Russia have been engaged in a diplomatic tit-for-tat for years, slowly shrinking the other's diplomatic mission in their respective countries by closing consulates, expelling diplomats or restricting visas -- with each side claiming the other took new action that prompted a response.

The U.S. mission in Russia is now running on a barebones staff, struggling to keep the embassy functioning. That's especially after Russia barred its citizens from working for the U.S. mission, which led the U.S. to shuttering all of its consulates in the country.

But the timing of Gorman's expulsion is notable, with tensions sky-high over a potential Russian invasion of Ukraine.

"We call on Russia to end its baseless expulsions of U.S. diplomats and staff and to work productively to rebuild our missions," the spokesperson said. "Now more than ever, it is critical that our countries have the necessary diplomatic personnel in place to facilitate communication between our governments."

-ABC News' Conor Finnegan

President Joe Biden told ABC News Chief White House Correspondent Cecilia Vega on Thursday morning that he believes Russian President Vladimir Putin will go through with an invasion of Ukraine within days.

Asked when departing the White House if it's his sense that an invasion would happen, Biden said, "My sense is this will happen in the next several days."

The president accused Russia of engaging in a "false flag operation" and said that despite the claims of pulling troops back, the Kremlin has actually moved more troops closer to Ukraine's border.

"They have not moved any of their troops out. They have moved more troops in," he said. "We have reason to believe that they are engaged in a false flag operation, to have an excuse to go in. Every indication we have is they're prepared to go into Ukraine and attack Ukraine."

Although he said he has not yet read Putin's written response to the U.S. and that he has no plans for a call with the Russian leader, Biden repeated that there is still a path open to diplomacy.

Russia insisted again Thursday that some troops massed near Ukraine are returning to base, far from the border.

Russian Ministry of Defense spokesman Igor Konashenkov said in a statement that units from the Western and Southern Military Districts, which were stationed in western Russia and Crimea, are now moving back to their permanent bases. He said Russian troops taking part in drills in Belarus will also return to base once they finish the exercises this weekend.

Konashenkov noted that the first units have already arrived in Nizhny Novgorod, Chechnya and Dagestan, hundreds of miles from the border with Ukraine.

-ABC News' Patrick Reevell

The United States has received a response from Russia regarding the discussion over Moscow's demands for security guarantees that NATO not expand, a senior official with the U.S. Department of State said Thursday.

"We can confirm that we have received a response from the Russian Federation," the official said. "It was delivered to Ambassador Sullivan in Moscow today."

The U.S. government, at Russia's insistence, sent written responses to two draft treaties Moscow published demanding guarantees that Ukraine will never join NATO and that the military alliance pull back its infrastructure from Eastern European countries that joined after the Cold War. Washington rejected those guarantees as non-starters but offered to discuss some confidence-building measures.

Russian Foreign Minister Sergey Lavrov said earlier Thursday that Moscow was planning to send its formal response to the Washington soon.

-ABC News' Conor Finnegan