Belarus' defense minister has announced that Russian troops will stay in the country, signaling an abrupt change in the Kremlin's plans.

The Kremlin had said the thousands of Russian troops would go home after joint exercises ended on Feb. 20. Now, they say troops will stay put and continue to "check" its forces amassed in the country.

Belarus Defense Minister Viktor Khrenin said the Russian troops would remain because of "increasing military activity on the eastern borders and the worsening situation in the Donbas" in eastern Ukraine.

Russia has massed an estimated 30,000 troops in Belarus for the joint war games "Allied Resolve," moving many of them thousands of miles from bases in Russia's far east.

The U.S. fears the Russian troops in Belarus — including tanks, attack helicopters, squadrons of fighter jets, airborne units, long-range heavy artillery and ballistic missiles — could be used to threaten Kyiv in the event of a Russian invasion. The Ukrainian capital is just a few hours drive from Belarus' southern border.

-ABC News' Patrick Reevell

Russian-controlled separatists in eastern Ukraine claimed on Sunday Ukrainian forces tried to storm some frontline positions in the separatist-held areas overnight and accused them of killing two civilians.

Ukraine has denied its forces have launched any attacks and the unverified claims came as Russia appeared to be intensifying its efforts to build a pretext to launch an invasion of Ukraine, by claiming it is coming to the defense of the separatists. Russian and separatist officials and media in the past four days have unleashed a barrage of false claims about Ukrainian attacks, including staging a fake bombing on a car in the separatists’ de facto capital, Donetsk.

The separatists claimed a Ukrainian airborne brigade attempted to storm their positions near the village of Pionerskoye, trying to force a river crossing there. They said five residential buildings were destroyed and that there are civilian casualties. They also claim to have fought off the Ukrainians, killing some.

The frontline in eastern Ukraine has been static for years and Ukraine is right now trying to avoid any actions that could give Russia an excuse to attack. Ukrainian troops have been ordered to largely hold fire, even if fired on.

The separatists and Russian state media are accusing Ukraine of preparing a major offensive, a claim that would align with Russia using a pretext to attack if it wants to.

-ABC News' Patrick Reevell

President Joe Biden will convene a meeting of his National Security Council Sunday to discuss the situation in Ukraine, White House press secretary Jen Psaki said in a statement.

Psaki said Biden "continues to monitor the evolving situation in Ukraine, and is being updated regularly about events on the ground by his national security team."

He was also updated on Vice President Kamala Harris' meetings at the Munich Security Conference, Psaki said. Harris addressed the conference Saturday afternoon and then met with Ukrainian President Volodymyr Zelenskyy. She also met with European Commission President Ursula von der Leyen, NATO Secretary General Jens Stoltenberg and the leaders of Germany, Greece, Estonia, Latvia and Lithuania.

-ABC News' Justin Gomez

U.S. Defense Secretary Lloyd Austin on Saturday told reporters in Lithuania he agrees with President Joe Biden that Russian President Vladimir Putin has made a decision to invade Ukraine.

“For months now, Russia has been building up its military forces in and around Ukraine, including in Belarus. They are uncoiling and are now poised to strike,” Austin said

Austin told reporters that there is still a diplomatic path to end the situation.

"Conflict is not inevitable, Mr. Putin can choose a different path,” he said.

"I believe that we should continue to try up until the very last minute until it's no longer possible,” he added later. “ But I think I think if you look at the stance that he is in today it's apparent that he has made a decision and that they're moving into the right positions to be able to conduct an attack.”

Austin said Russia has the military capability in the region "to move anytime he chooses."

As he told Martha Raddatz in her exclusive interview on Friday, those forces include not only combat forces, but logistics, combat aviation, field hospitals and command and control operations.

The U.S. currently has 100 American troops in Lithuania and it appears that a major topic of discussion between the two leaders was setting up a permanent American military presence in the Baltic country. Austin said he had no announcements to make about the possibility but Lithuania's Minister of National Defense Arvydas Anušauskas acknowledged that the topic took up much of their discussion.

-ABC News' Luis Martinez

In response to a plea on Twitter from a Ukrainian official, SpaceX CEO Elon Musk said Saturday that his high-speed internet service Starlink is now active in Ukraine.

"More terminals en route," he tweeted in a reply to Mykhailo Fedorov, Ukraine's vice prime minister and minister of digital transformation.

Earlier Saturday, Fedorov appealed directly to Musk and asked him to provide Ukraine with Starlink stations.

The terminals are small, portable satellite dishes on Earth that connect directly to Starlink satellites in space -- providing high-speed internet to rural and hard-to-reach locations. This is especially important for areas that have already lost access and could potentially help them avoid cyberattacks.

-ABC News' Gio Benitez