United States Ambassador to the United Nations Samantha Power told the U.N. on Thursday that Western nations would need to “ratchet up the consequences on Russia” in the wake of Russian forces invading Ukraine.

“Russia is not listening,” Power said at a U.N. Meeting Thursday. “Instead of listening, instead of heeding the demands of the international community and the rules of the international order, at every step, Russia has come before this council to say everything except the truth. It has manipulated. It has obfuscated. It has outright lied. So we have learned to measure Russia by its actions and not by its words.”

Earlier Thursday, senior Ukrainian and NATO officials said at least 1,000 Russian troops had crossed into southeastern Ukraine, drawing widespread international condemnation and once again putting the U.S. and the Kremlin at odds.

Power took direct aim at Russian President Vladimir Putin in her fiery remarks to the U.N.

“The mask is coming off,” she said. “In these acts — these recent acts — we see Russia’s actions for what they are: a deliberate effort to support, and now fight alongside, illegal separatists in another sovereign country."