U.S. Will 'Respond Aggressively' if Russia Uses Chemical Weapons: Envoy

U.S. Ambassador to the United Nations Linda Thomas-Greenfield warned on Sunday that the U.S. will "respond aggressively" if Russia uses chemical weapons in Ukraine.

"We've been clear, if they escalate to this level, we will respond aggressively to what they are doing," she said during an interview with CNN host Jake Tapper on State of the Union. "You've seen the consequences so far of our actions against Russia and against Putin, and they are feeling those consequences, and they will feel more if they take this unfortunate decision to use chemical weapons."

Her remarks come as the U.S., NATO, and Ukraine expressed their concerns about a possible Russian false flag operation that would justify their use of chemical weapons in the Eastern European country.

"The Russians came to the Security Council on Friday with the spurious accusations that the U.S. was supporting Ukraine's chemical weapons programs. And I'm not going to give that any more amplification here. What we see happening is, again, this is a false flag effort by the Russians," she said.

The U.N. Ambassador further explained that the Russians are "advancing what they might intend to" before they could potentially use chemical weapons.

"We've seen that happen before. They are the ones who've used chemical weapons. They used them in Syria. They've used chemical weapons against their own people. And we are concerned that they may use chemical weapons in Ukraine," she added.

Republican Wyoming Representative Liz Cheney also warned on Sunday against consequences that Russia could face if "brutality" increases in Ukraine.

During an interview on NBC News' Meet the Press, co-host Chuck Todd asked Cheney if there is "a red line in your mind for whether NATO should at least intervene to protect civilians in some form in Ukraine" if chemical weapons were used.

"I think that it should be, Chuck," she responded. "And I think that we in the west, the United States and NATO, we need to stop telling the Russians what we won't do. We need to be very clear that we are considering all options, that the use of chemical weapons is certainly something that would alter our calculations."

"And they [Russia] need to understand that if the brutality here increases, the United States will contemplate and consider every possible range of actions along with our NATO allies," she added.

Cheney continued: "I think it's important that they know that we will contemplate changing the calculation in terms of humanitarian challenges and the humanitarian devastation the Ukrainian people are facing."

On March 9, the U.S. warned against the use of chemical weapons in Ukraine after Russia alleged that the U.S. has secret biological weapons in the Eastern European country.

"Now that Russia has made these false claims, and China has seemingly endorsed this propaganda, we should all be on the lookout for Russia to possibly use chemical or biological weapons in Ukraine, or to create a false flag operation using them. It's a clear pattern," White House press secretary Jen Psaki said in a series of tweets.

US officials warn against Russia chemical attack
U.S. Ambassador to the UN Linda Thomas-Greenfield and Republican Rep. Liz Cheney warned about consequences if Russia uses chemical weapons in Ukraine. Above, a man walks between buildings and homes that have been damaged by Russian airstrikes in the Ukrainian city of Bila Tserkva on March 8. Photo by ARIS MESSINIS/AFP via Getty Images