U.S. President Joe Biden will meet with the National Security Council on Sunday, the White House announced Saturday as it reaffirmed that “Russia could launch an attack against Ukraine at any time,” White House press secretary Jen Psaki said.

Psaki said Biden was briefed Saturday on Vice President Kamala Harris’ meetings at the Munich Security Conference. Harris met Saturday with Western leaders, among them NATO Secretary-General Jens Stoltenberg, European Commission President Ursula von der Leyen, and German Chancellor Olaf Scholz, as well as Ukrainian President Volodymyr Zelenskiy.

Biden to Huddle with National Security Council Sunday on Ukraine

Russian President Vladimir Putin presided over military drills Saturday as shelling escalated in eastern Ukraine.

Biden to Huddle with National Security Council Sunday on Ukraine

Observers from the Organization for Security and Cooperation in Europe reported more than 1,500 cease-fire violations in east Ukraine on Saturday, the highest single-day number this year.

Biden to Huddle with National Security Council Sunday on Ukraine

Russia’s defense ministry said Saturday’s exercises, which the Kremlin says were previously planned to check readiness, involved practice submarine launches of intercontinental ballistic missiles, with Putin and the president of Belarus looking on.

Saturday, U.S. Defense Secretary Lloyd Austin said the more than 150,000 Russian troops that have massed at Ukraine’s border “are now poised to strike,” as he spoke with reporters in Lithuania, where Lithuanian President Gitanas Nauseda called for an increased U.S. troop presence.

At the Munich Security Conference, Harris warned that Russia’s plan was already unfolding.

“There is a playbook of Russian aggression, and this playbook is too familiar to us all. Russia will plead ignorance and innocence. It will create false pretext for invasion, and it will amass troops and fire power in plain sight,” said Harris, who added a Russian invasion would trigger sanctions that include far-reaching financial sanctions and export controls.

She also said the U.S. would bolster NATO’s eastern flank as another deterrent to a Russian military invasion.

Speaking at the conference earlier Saturday, Stoltenberg said Russia, in threatening Ukraine, “will get more NATO” instead of the smaller NATO footprint Putin says he is seeking.

Stoltenberg also said he has sent a letter to Russian Foreign Minister Sergey Lavrov calling for a meeting of the NATO-Russia Council to avert a conflict in Ukraine. Stoltenberg told the Munich Security Conference that there is no evidence that Russia has withdrawn any of its troops from Ukraine’s borders and there is a real risk of conflict.

"We are extremely concerned because we see that they continue to build up, they continue to prepare. And we have never in Europe seen since the end of the Cold War, such a large concentration of combat-ready troops," Stoltenberg said.

Ukraine’s Zelenskiy met on the sidelines with Harris, as he sought to rally more military and financial support from Western allies.

As he addressed the audience of high-level officials and security experts from around the world, Zelenskiy pushed back against U.S. predictions of an imminent Russian invasion, declaring “We do not think we need to panic,” Agence France-Presse reported.

British Prime Minister Boris Johnson, however, told the BBC that evidence points to Russia planning "the biggest war in Europe since 1945.”

Ukraine’s military accused separatists in two breakaway territories in eastern Ukraine – the self-proclaimed Donetsk and Luhansk republics – of carrying out a new wave of attacks Saturday.

The separatists, who also accused Ukraine’s military of carrying out new attacks Saturday, signed mass military mobilization decrees. The head of one of the territories urged all able-bodied men to take up arms against what he claimed is Kyiv’s aggression. The regions have also begun evacuating some civilians from border areas.

Biden said the move was a result of Russian misinformation, saying that it “defies basic logic” that people in Ukraine would “choose this moment” to engage in combat with more than 150,000 Russian troops on Ukraine’s borders.

Ukraine’s military said two of its soldiers were killed Saturday in shelling from pro-Russian separatists in eastern Ukraine, according to AFP, after initially reporting one fatality.

Should Moscow invade Ukraine, it will be critical for the United States to convince the world that Russia is the aggressor and that it did so unprovoked, Max Bergmann, senior fellow at the Center for American Progress, told VOA.