PM In 'Robust Exchange' With Putin On Ukraine David Cameron has warned Vladimir Putin that he needs to implement a peace deal designed to de-escalate Ukraine's crisis or future relations with the West are threatened. The Prime Minister confronted the Russian President on the fringes of the G20 summit in Brisbane, Australia, over Moscow's interference in its smaller neighbour. David Cameron meets Vladimir Putin Moscow is accused of having its own troops and tanks in Ukraine and failing to live up to the terms of the Minsk deal signed by the Ukrainians, Russians and pro-Moscow separatists in September. Mr Cameron said Mr Putin's exercise of "international machismo" should not be allowed to distract from events in Ukraine, where violence has continued despite a ceasefire. Video: Cameron Warns Russia Over Ukraine And he said Russia could expect a "firm" response from the European Union if the Minsk agreement was violated. In what was described as a "robust exchange," Mr Putin was warned by the PM he faces a "fork in the road." The Kremlin, for its part, said that Mr Putin - who reportedly plans to leave the summit early - and Mr Cameron expressed a mutual interest in seeing Russia and the West mend fences at the closed-door meeting. "Vladimir Putin and David Cameron noted interest in restoring ties between Russia and the West and adopting efficient measures to settle the Ukraine crisis which will facilitate the renunciation of confrontational sentiments," the Kremlin said in a statement. But Downing Street made it clear that Britain's response will depend on developments on the ground in eastern Ukraine. Gallery: Australian PM Greets G20 Leaders Australian Prime Minister Tony Abbott has welcomed leaders of the world's top industrialised nations at the G20 summit. There was a smile from David Cameron as the pair shook hands Meanwhile, Mr Putin received a frosty welcome from Stephen Harper when he approached the Canadian Prime Minister for a handshake in Brisbane. "I guess I'll shake your hand, but I have only one thing to say to you: You need to get out of Ukraine," Mr Harper told Mr Putin, according to Mr Harper's spokesman, Jason MacDonald. Mr MacDonald said Mr Putin "did not respond positively," but declined to give further details of the tense exchange. The Russian leader has a choice between restoring relations with the rest of the world by observing the terms of the Minsk agreement or risking further sanctions by continuing to destabilise Ukraine. A Downing Street source said: "We can either see implementation of the Minsk agreement and what follows from that in terms of an improvement of relations. Gallery: Australia Hosts G20 Protesters wearing masks depicting G20 leaders call for global equality among nations outside the site of the venue of the annual G20 leaders summit in Brisbane in Queensland Or we can see things go in a very different way in terms of relations between Russia and the UK, Europe and the US. But Mr Putin continued to insist that Russia has no troops in eastern Ukraine, the source said. President Barack Obama described the US as a leading voice in opposing Russia's aggression in Ukraine, which he said was "a threat to the world." In a speech to a Brisbane university audience, Mr Obama referred to the shooting down in July of a Malaysia Airlines plane by a missile suspected to have been fired by Russian-backed rebels in Ukraine, which killed the loss of 298 lives, including 38 Australian citizens and residents. "As your ally and friend, America shares the grief of these Australian families and we share the determination of your nation for justice and accountability," Mr Obama said.