BRISBANE (REUTERS) - Russian President Vladimir Putin said on Sunday that there was a "good chance" of resolving the conflict in Ukraine as Western leaders squarely blamed Moscow and threatened to slap more sanctions if it did not take action to end the crisis.

Putin was speaking at a G-20 leaders summit in Brisbane where he has come under intense pressure, with Canadian Prime Minister Stephen Harper telling him to "get out of Ukraine".

The leaders of the United States, Japan and Australia vowed to oppose Russian aggression, and European leaders including German Chancellor Angela Merkel have warned of more sanctions unless Russia withdraws troops and weapons from Ukraine and ends its support for pro-Russian separatist rebels.

The crisis has taken relations between Russia and the West a post-Cold War low.

Sanctions aimed at sectors like oil and banking, as well as individuals close to Putin, are squeezing Russia's economy at a time when falling oil prices are straining the budget and the rouble has plunged on financial markets.

Elsewhere at the summit, the United States and other nations overrode host Australia's attempts to keep climate change off the formal agenda. The communique at the end of the meeting will include a significant passage on climate change, EU officials said.

Russia has denied any involvement in the conflict in Ukraine that has killed more than 4,000 people this year.

"Today the situation (in Ukraine) in my view has good chances for resolution, no matter how strange it may sound, but certain structures had been established on both sides that could handle the tasks they are facing better," Putin told reporters before he left Brisbane ahead of the formal ending of the summit.

US President Barack Obama, Australian Prime Minister Tony Abbott and Japanese Prime Minister Shinzo Abe lined up together against Russia on Sunday, vowing to oppose what they called Moscow's efforts to destabilise eastern Ukraine.

Speaking after a rare trilateral meeting on the sidelines of the summit, the three said they would oppose "Russia's purported annexation of Crimea and its actions to destabilise eastern Ukraine", and were committed to "bringing to justice those responsible for the downing of Flight MH17." The Malaysian Airlines flight was shot down over Ukraine earlier this year.

Obama is due to meet European leaders to discuss Ukraine later in the day and EU foreign ministers will meet on Monday to consider further steps, including additional possible sanctions on Russia.