Russia can expect a "firm" response from the European Union if it fails to live up to the terms of a peace deal designed to bring an end to conflict in Ukraine, David Cameron has warned.
The Prime Minister is expected to meet Vladimir Putin today on the fringes of the G20 summit in Australia, which is officially focusing on economic growth and jobs but is rapidly developing into a showdown between the Russian president and other leading world powers.
Mr Putin has stoked up tensions at the Brisbane gathering by deploying a task force of warships to the Coral Sea off the coast of Queensland, in what Australian PM Tony Abbott described as part of a "regrettable pattern" of Russian military assertiveness which appeared to be trying to recreate the "lost glories" of the Soviet Union.
Mr Cameron gave short shrift to the Russian display of force, joking with reporters: "I didn't feel it necessary to bring a warship myself to keep myself safe at this G20, and I'm sure that Putin won't be in any danger."
Mr Abbott, who is hosting the gathering of the world's 20 leading economies, has called for an apology from Russia for the downing of the Malaysia Airlines jet MH17 over Ukraine, which killed 38 Australians in July.
And Mr Cameron has made clear he will 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.
Following former Soviet president Mikhail Gorbachev's warning that Mr Putin was pushing the world towards a new Cold War, Mr Cameron said that the international community would not simply "move on" from events in Ukraine, and held out the prospect of further EU sanctions if Russia continues to take the wrong path.
The PM declined to speculate on what form future sanctions might take, but said: "What I think Europe has shown, and Britain's played a leading part in this, is that every time there's been a step in the wrong direction - whether that was an illegal referendum in Crimea, whether it was the incursion of Russian troops, whether it was destabilisation - every time there's been a step in the wrong direction, Europe has taken a step in a firm direction."
Speaking to reporters in Brisbane, Mr Cameron 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."
He added: "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, to 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.
"That's not something I want to see happen, but I think Russia needs to know that this can't be like what happened in the past with other frozen conflicts, where the world has moved on. I don't think the world can move on from what's happened in Ukraine."
Mr Cameron said that EU sanctions against key members of Mr Putin's inner circle as well as sectors of the Russian economy have had an effect on the value of the rouble, the Moscow stock market and the ability of Russian banks to access international finance.
"Russian action in Ukraine is unacceptable," he said. "We have to be clear about what we are dealing with. It is a large state bullying a smaller state in Europe."
In an apparent reference to the build-up to the Second World War, the PM added: "We have seen the consequences of that in the past and we should learn the lessons of history and make sure we don't let it happen again."
The sanctions regime is on the agenda for a meeting of EU foreign ministers in Brussels on Monday, though at present any expansion of the action is thought likely to be restricted to members of pro-Russian rebel groups in eastern Ukraine.
Mr Putin's invitation to Brisbane has sparked protests by Ukrainian groups - as well as a counter-demonstration by members of Australia's Russian expat community.
And the Australian press has reacted with fury to the deployment of the Russian cruiser Varyag and three support vessels, with one popular newspaper splashing Mr Putin's face in front of a Cold War-era Soviet hammer and sickle on its front page.
Speaking alongside Mr Cameron at a pre-summit press conference in Canberra, Mr Abbott said that, while investigations continue into the MH17 disaster, "it is our clear understanding on the evidence so far that clearly this was shot down by Russian-backed rebels, most likely using Russian-supplied equipment, so I think there is a heavy responsibility on Russia to come clean and atone".
The Australian PM, who spoke to Mr Putin at this week's Asia-Pacific APEC summit in Beijing, said: "One of the points that I tried to make to President Putin is that Russia would be so much more attractive if it was aspiring to be a superpower for peace and prosperity, if it was trying to be a superpower for ideas and for values instead of trying to recreate the lost glories of tsarism or the old Soviet Union."
He added: "It is part of a regrettable pattern. Whether it's the bullying of Ukraine, whether it's the increasing Russian military aircraft flying into the airspace of Japan and European countries, whether it's the naval task group which is now in the South Pacific, Russia is being much more assertive than it has been for a very long time.
"Interestingly, Russia's economy is declining even as Russia's assertiveness is increasing."
TUC general secretary Frances O'Grady warned that the official G20 agenda of boosting global economic growth risked sidelining the challenges being faced by ordinary workers around the world who have seen real wages and living standards fall.
Speaking in Brisbane, Ms O'Grady said: "This G20 will go down in history as an irrelevant talkfest unless leaders get to grips with the real challenges facing ordinary families.
"The same old trickle-down economics with no plan to ensure workers get fair shares of growth offers little hope to millions of families struggling to make ends meet.
"People have lost faith in politicians who seem to think that more insecure and zero-hours jobs count as a success, and who have abandoned the promise of making work pay. Growth cannot be delivered without a boost in demand which in turn requires a much-needed boost in pay packets.
"Perhaps if David Cameron and fellow leaders spent less time in the summit bubble talking to hedge fund bosses and business chiefs, and more time out in the real world listening to workers, we would get the plan for decent jobs and the sustainable growth that people want to see."