Russia's parliament voted for a law on Tuesday that calls on President Vladimir Putin to recognize two Russian-controlled breakaway regions in eastern Ukraine as independent.

The measure is a formal appeal to Putin to recognize the self-declared Donetsk and Luhansk people's republics, in an area of southeastern Ukraine known as the Donbas, where Russian-backed separatists forces have been battling the Ukrainian army since 2014.

Such recognition would open a path for Russia to formally annex the two regions as it did the Crimean Peninsula almost eight years ago. It's now up to Putin to decide whether to go through with it.

Two bills were initially put forward for a vote in Russia's parliament -- one by the Communist Party and the other by Putin's ruling United Russia. The first would have the request sent to the president immediately, while the second would have sought consultations with the foreign ministry and other government agencies before appealing directly to Putin. Ultimately, parliament voted for the first bill.

Ukrainian President Volodymyr Zelenskyy's office called the vote an "escalatory action." Ukraine’s foreign ministry has warned that it will consider Russia recognizing the separatist regions as a withdrawal from the Minsk peace agreement reached in 2015, which was supposed to end the conflict in Donbas that broke out a year earlier.

-ABC News' Patrick Reevell

Ukrainian Minister of Foreign Affairs Dmytro Kuleba reacted to Russia's announcement Tuesday that it is withdrawing some troops from the border, saying his country will "believe it when we see it."

"There are constantly various statements coming from the Russian Federation, so we have a rule: we’ll believe it when we see it," Kuleba said during a televised briefing Tuesday. "When we see the withdrawal, we’ll believe in de-escalation."

-ABC News' Patrick Reevell

Some Russian troops positioned near the border with Ukraine will begin returning to their bases Tuesday after completing "exercises," according to the Russian Ministry of Defense.

The units set to return are from Russia's Southern and Western Military Districts, the defense ministry said Tuesday. But there are troops from other military districts massed on the border. Still, if some troops do pull back, it would potentially be a key signal that the crisis with Ukraine will not escalate.

Russian state media then released video purportedly showing tank troops loading up in neighboring Belarus to return home as well as tanks in southwestern Russia moving back. A spokesperson for Russia's Southern Military District told state media Tuesday that some personnel have begun leaving Crimea for their permanent bases following the completion of drills. In 2014, Russia annexed Ukraine's Crimean Peninsula and established two federal subjects there, the Republic of Crimea and the federal city of Sevastopol. But the international community still recognizes the territories as being part of Ukraine.

Russian Minister of Defense Sergey Shoygu told Russian President Vladimir Putin on Monday that the military exercises would end "in the near future." There are still drills being conducted in neighboring Belarus as well as the Black Sea that are due to end Feb. 20.

Maria Zakharova, spokesperson for the Russian Ministry of Foreign Affairs, said in a post on her official Facebook page on Tuesday that Feb. 15 "will go down in history as the day the Western propoganda war failed."

"Disgraced and destroyed without a single shot fired," Zakharova added.

-ABC News' Patrick Reevell

While the United States believes a path of diplomacy remains "open" to Russia, a White House official warned that a Russian invasion of Ukraine "could begin at any time."

Answering a question from ABC News' Cecilia Vega during a press briefing Monday, White House Principal Deputy Press Secretary Karine Jean-Pierre said the U.S. government is so far seeing "more and more" Russian troops arrive on the border with Ukraine.

"In the past 10 days or so, when you look at what is happening at the border of Ukraine, there, we are seeing more than 100,000 troops there and it's just been an every day more and more troops," Jean-Pierre said.

"So we are certainly open to having conversations and seeing a de-escalation," she added. "That door is open for diplomacy and this is up to President Putin. He has to make that decision. It is his decision to make on which direction he wants to take this."

Jean-Pierre noted that "it remains unclear which path Russia will choose to take."

When asked about the imminency of the situation, she said: "We are in the window when an invasion could begin at any time."

"I'm not going to comment on the intelligence information," she added, "except to say that it could begin this week."

-ABC News' Ben Gittleson