Russian President Vladimir Putin plans to leave the G20 summit early, a member of his delegation said, after Western leaders blasted Moscow on Saturday for the crisis in Ukraine and threatened more sanctions.

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.

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 MinisterStephen Harper.

"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 Moscowwithdraw troops and weapons from the neighbouring 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 centre 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."

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 G20 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 inBrisbane, Putin was met by the assistant defence 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.

ONLY TOPIC DISCUSSED

A Kremlin spokesman said the Ukraine crisis was the only topic discussed at a one-on-one meeting between Putin and British Prime Minister David Cameron, but he added both expressed interest in "ending confrontation" and rebuilding relations. Putin also met French President Francois Hollande, and both agreed to protect their ties from the effects of sanctions, the spokesman said.

Outside the summit, Ukrainian Australians staged an anti-Putin protest, wearing headbands reading "Putin, Killer".

Draped with the flags of the nations that lost citizens when the flight MH17 was shot down, the demonstrators lay on a large Ukrainian flag, in what they said was a protest at the "murderous acts" Russia's president was responsible for.

G20 host Australia had hoped that the two-day summit would focus on global economic growth, not security or the environment.

Obama also said the United States would renew commitment to its strategic pivot to the Asia-Pacific in comments seen as a veiled warning to China.

Obama insisted that Asia's security order must not be based on "coercion or intimidation ... where big nations bully the small, but on alliances for mutual security".

He did not explicitly point the finger at China, but there was little doubt that he was alluding to Beijing's maritime disputes and growing concern about its military build-up.

Despite Australia's reluctance to allow climate change on the summit agenda after it abolished a tax on carbon emissions, Obama spent a large part of his speech urging action on the environment. He pledged a $3 billion U.S. contribution to an international fund to help poor countries cope with the effects of climate change.

But Australia stuck to its economic script.

A plan to increase global economic growth by an additional 2 percentage points over the next five years was on track, Australian Treasurer Joe Hockey said.

"This ambition translates into about $2 trillion in additional global economic activity and millions of new jobs," he said.