American TV comedian Stephen Colbert was joking about invading Saskatchewan this week — prompting a quick response from Premier Brad Wall.

"Back off, Colbert," Wall tweeted on Tuesday.

On Monday night, Colbert was interviewing Michael McFaul, former U.S. ambassador to Russia, who observed that Vladimir Putin's popularity has gone up in response to recent moves in Ukraine.

Faul noted that Putin's approval rating in his own country is now around 80 per cent, while Obama's is around 40.

"Maybe Obama should invade ... Saskatchewan, something like that," Colbert said.

"I don't think that would be wise," McFaul replied.