WASHINGTON (NEXSTAR) — Russian President Vladimir Putin continues to put pressure on the United States and its NATO allies. With thousands of Russian troops massed on the border of Ukraine, Putin is threatening military action.

“Vladimir Putin right now is flexing,” Rep. John Joyce (R-Penn.) said.

Joyce says the U.S. needs to stand up against Putin. On Sunday, the Russian president demanded that the U.S. and its NATO allies back off, or else.

“Like I already said, they deploy missile systems in Ukraine that can reach Moscow in four to five minutes. Where should we move? They have taken it to the point where we simply must tell them ‘stop,'” Putin said.

Putin says he wants NATO missiles out of Eastern Europe and wants a promise that Ukraine will not be allowed to join NATO. Putin has amassed thousands of Russian troops on the border of Ukraine. Defense analysts say Russia could be preparing for military action sometime after the first of the year.

“We cannot allow Putin to be aggressive in this arena,” Joyce said. “This is a geopolitical force and we need to be with our friends and we need to be with our allies, recognizing that not just the Ukraine but Poland is in that area.”

Joyce says the U.S. has earmarked $300 million in military assistance for Ukraine in the National Defense Authorization Act.

“I hope these funds, that these military supplies aren’t needed, but we need to let our friends and our allies know that we will stand with them,” Joyce said.