Russian President Vladimir Putin has come under intense pressure from the West over Moscow's alleged support for separatist fighters in eastern Ukraine at the G20 summit in Australia.

In unusually frank language between two leaders, Stephen Harper, the Canadian prime minister, was reported to have told Putin as they shook hands on Saturday to "get out of Ukraine".

According to Jason MacDonald, Harper's spokesman, the prime minister told the Russian leader: "I guess I will shake your hand but I have only one thing to say to you: You need to get out of Ukraine."

British Prime Minister David Cameron was among other leaders who publicly criticised Russia, accusing it of "bullying a smaller state in Europe" and warning that Moscow would face further sanctions if it continues "destabilising Ukraine".

Speaking on Saturday on the sidelines of the two-day summit in Brisbane, Cameron told the UK's Sky News: "I am very frank when I meet with him [Putin] that the things that Russia has done in Ukraine are unacceptable."

During a closed-door meeting between Cameron and Putin, the British leader warned that the Russian leader had a choice to make, according to sources quoted by British media.

"The prime minister was clear at the start of the Ukraine discussions that we face a fork in the road, in terms of where we go next," the UK source reportedly said.

'Hindering economic growth'

German Chancellor Angela Merkel told reporters that the tensions over Ukraine were hindering efforts to boost economic growth.

"It's clear that these geopolitical tensions, including relations with Russia, are not really conducive to promoting growth," she said. "We are all striving to do everything diplomatically possible to see improvements."

EU foreign ministers will meet on Monday to assess the situation in Ukraine and whether further steps including additional sanctions are needed against Russia, said European Council President Herman Van Rompuy. Obama plans to meet European leaders to discuss the matter on Sunday, he added.

Meanwhile, Putin said that Russia will not allow the Ukraine government to "destroy" its political opponents and adversaries in east Ukraine.

"The most important thing is that one does not have a one-sided view of the problem," Putin said in a first brief excerpt of the interview that was broadcast by German television network ARD.

The full interview will be broadcast on Sunday evening.

"Today there is fighting taking place in the east of Ukraine, the Ukrainian government has deployed troops there," Putin told ARD, which said the interview was conducted on Thursday evening in Vladivostok.

"There have even been missiles fired, but is that mentioned? There's not been a word on that.

"That means, that you [the Western media] want the Ukrainian government to destroy everything there, including all their political opponents and adversaries.

"Is that what you want? That is not what we want and we will not allow that to happen."

Kiev has accused Russia of sending soldiers and weapons to help separatist rebels in eastern Ukraine to launch a new offensive in a conflict that has killed more than 4,000 people.

Russia has denied it is involved in the recent escalation in fighting in its neighbour.