Vladimir Putin feels he has to 'up the ante' amid Ukraine's pushback

ANU's Professor John Blaxland says Vladimir Putin - amid the pushback from Ukrainians - feels he has to "up the ante" by threatening to use nuclear weapons.

Professor Blaxland told Rita Panahi he thinks this threat should be taken "very seriously".

"There's no question that we've seen Vladimir Putin happily use polonium, he's used all sorts of bioweapons against his own citizens, he's a man who's remarkably ruthless and when he says he'll do something like this, I think he means it.

"There's a real worry here that Vladimir Putin, having not quite been as successful in the first few days of this campaign as he might've hoped ... he's now feeling, 'well I've got to up the ante'."