The Russian official told Reuters that Putin planned to skip a working session on Sunday at the two-day summit in Brisbane and bring forward his departure because he needed to attend meetings in Moscow.

Russian President Vladimir Putin plans to leave the G-20 summit early, a member of his delegation said, after Western leaders blasted Moscow on Saturday for the crisis in Ukraine and threatened more sanctions.

Russia denied it was involved in a recent escalation of military activity in Ukraine, where fighting has claimed more than 4,000 lives, but faced strong rebukes from Western leaders, including U.S. President Barack Obama and Canadian Prime Minister Stephen Harper.

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"I guess I'll shake your hand but I have only one thing to say to you: you need to get out of Ukraine," Harper told Putin at the summit, according to his spokesman Jason MacDonald.

Putin's response to the comment wasn't positive, MacDonald said in an email, without elaborating.

Obama said Russian aggression against Ukraine was a threat to the world, while the European Council demanded Moscow withdraw troops and weapons from the neighboring nation and put pressure on rebels there to accept a ceasefire.

Speaking on the sidelines of the summit, Obama placed security and climate change at the center stage of the leaders meeting, overshadowing talks on how to lift flagging global economic growth.

Obama said the United States was at the forefront of "opposing Russia's aggression against Ukraine, which is a threat to the world, as we saw in the appalling shoot-down of MH17".

German Chancellor Angela Merkel said the European Union was considering further financial sanctions against Russian individuals because of the crisis in Ukraine.

"The present situation is not satisfying," Merkel told reporters at the summit. "At present the listing of further persons is on the agenda."

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Europe's foreign ministers will meet on Monday to assess the situation in Ukraine and whether further steps including additional sanctions were needed against Russia, said European Council President Herman Van Rompuy.

Putin's isolation at the G-20 summit was also evident with his placing on the outer edge for the formal leaders photograph. While Obama and Chinese Premier Xi Jinping were met by Australia's governor general and attorney general when they arrived in Brisbane, Putin was met by the assistant defense minister.

Despite being under intense pressure, Putin was all smiles, shaking hands with host Australian Prime Minister Tony Abbott, who had threatened to "shirt front", or physically confront, him over the downing of Malaysian airliner MH17 over Ukraine, in which 28 Australians died.