Tony Abbott says Russia is a "bully" that is threatening global security and has indicated that he may rethink his intention to invite its President Vladimir Putin to the G20 summit in Brisbane this year.

Registering Australia's rejection of Russia's militarism in Ukraine, the Prime Minister endorsed Canadian counterpart Stephen Harper's description of Mr Putin as an "extreme nationalist" and an "imperialist".

"They're very forthright remarks and I think they're perfectly appropriate remarks for the Canadian Prime Minister to make," Mr Abbott said in Ottawa yesterday.

"Let's not minimise the affront to international stability and the affront to the ordinary norms of behaviour between nations which Russia's been responsible for.

"It's bitten off the Crimea. It's obviously interfering in Ukraine and this should stop. This should stop. No country has a right to bully another country just because it can."

Mr Harper, who Mr Abbott said was a "beacon" to centre-right political parties, told Canadian TV that Eastern European leaders were "beside themselves" with alarm at Russia's activities in Ukraine.