Michael McFaul, the former U.S. ambassador to Russia, has been outspoken in his criticism of Russian President Vladimir Putin ever since Russian forces seized Ukraine’s Crimea Peninsula earlier this year. But he stepped up his rhetoric significantly on Tuesday, suggesting that the United States should arm the Ukrainian military so it is better equipped to fight Russian-backed separatists in eastern Ukraine. “If Putin can arm rebels,” McFaul asked, “why can’t we arm Ukraine?”

The message has been retweeted more than 450 times in less than three hours, with some questioning whether that would escalate tensions between Washington and Moscow in a way that wouldn’t be wise for U.S. interests:

McFaul’s tweet actually was the second in a series questioning the West’s strategy in dealing with Putin. Here’s the first:

McFaul, who

in Moscow in February after two turbulent years, didn’t back down when questioned on his views. He quickly responded when a critic said it was “unbelievable” he was the former U.S. ambassador to Russia and a Stanford University professor.

Then he continued his criticism:

I reached out to McFaul for clarification on his tweets this afternoon. What arms does he think would help Ukraine? Does he see it having any specific needs? Would U.S. military advisers have to deploy to train Ukrainian soldiers to use the new equipment? Would sending weapons to Ukraine create a proxy war between Washington and Moscow? McFaul said in an e-mail that does not consider himself “an expert on such issues,” and was responding to an earlier discussion with some Russians.

“If Putin feels free to arm the insurgents I do not understand why they think it is ‘illegal’ or improper for the West support a government recognized by the world (including Russia) as the legitimate authority in Ukraine,” McFaul said. “Second, this first step must be for the Ukrainians to request such assistance. Only after then would the U.S. and NATO have to wrestle with the questions you raise.”

He concluded: “If Russians don’t want the West to provide military assistance to Ukraine, then they should stop providing arms to insurgents.”