World leaders are meeting in Australia for the first day of this weekend's G20 summit, with the crisis in Ukraine expected to dominate discussion at the talks despite the issue not being on the official agenda.
At the summit, the International Monetary Fund has announced a €237m package to help fight Ebola in west Africa.
The IMF package involves a combination of loans, debt relief and grants for Liberia, Sierra Leone and Guinea.
Meanwhile, Vladimir Putin is expected to face a hostile reception from some western leaders who are concerned about Russia's military assertiveness.
President Obama says Russia is a threat to the world, highlighting flight MH17 which was shot down over eastern Ukraine by pro Russian separatists:
David Cameron says Russia could expect a "firm" response from the European Union if Moscow violated a peace deal designed to end the Ukraine conflict.
Mr Cameron vowed to confront Mr Putin over Russia's failure to live up to the terms of a peace deal signed by Ukraine, Russia and pro-Moscow separatists in Minsk in September.
Speaking to reporters in Brisbane, he said: "I hope it's possible to stand by the Minsk agreement.
"It's not a perfect agreement from anyone's point of view, but it has some key parts to it, about Russian troops and about borders and about respecting Ukraine's sovereignty. I think there's a very clear choice for Russia of which path it takes.
"If it takes the Minsk path we could progressively see normalisation of relations between Russia and Ukraine, you could see Ukraine's sovereignty and elections respected, you could see the removal of sanctions if that were to happen.
"But the other path of not respecting the Minsk agreement, continuing to undermine Ukrainian sovereignty, continuing to see Russian troops in Ukraine and Russian tanks and the rest of it - I don't think Europe would have a choice but to maintain the sanctions we have."
He added that if Russia violates the peace deal, the EU will "start looking at further measures that could be taken if Russia takes further steps and to putting relationships between European countries and Russia on a very different basis".
Heightened tensions
World leaders are gathering in Brisbane to talk about economic growth and jobs, but tensions between Moscow and the West have dominated the lead-up to the talks.
Mr Putin has heightened tensions by deploying a task force of warships to the Coral Sea off the Queensland coast, in what Australian Prime Minister Tony Abbott described as part of a "regrettable pattern" of Russian military assertiveness.
Mr Abbott has called for an apology from Russia for the downing of the Malaysia Airlines jet MH17 over Ukraine in July, which killed 38 Australians.
Speaking alongside Mr Cameron at a pre-summit news conference in Canberra, Mr Abbott said: "It is our clear understanding on the evidence so far that clearly this (plane) was shot down by Russian-backed rebels".
He added that there "is a heavy responsibility on Russia to come clean and atone" for the tragedy.
Originally posted at 7.22am
