The United States continues to warn that Russia could invade Ukraine “any day” amid escalating tensions in the region, with President Joe Biden telling reporters Thursday that the threat is now “very high.”

U.S. Secretary of State Antony Blinken on Thursday, making urgent remarks to the United Nations Security Council, challenged Moscow to commit to no invasion.

More than 150,000 Russian troops are estimated to be massed near Ukraine’s borders, U.S. officials have said. While Russian President Vladimir Putin and the Kremlin claim that some troops have begun to withdraw, Biden told reporters that more Russian forces have moved in, contrary to Moscow’s claims.

It remains unclear whether Putin has made a decision to attack his ex-Soviet neighbor.

Russia has denied any plans to invade and reiterated its demands that the U.S. and NATO bar Ukraine from joining the military alliance.

Abc