G20 summit set for showdown between Western leaders and Putin

A showdown between Western leaders and Russian President Vladimir Putin is likely at the G20 summit which starts in Australia today, following fresh reports of Russian troops pouring into eastern Ukraine.

US President Barack Obama meanwhile plans three-way talks with Japan and Australia on the summit's sidelines, looking to shore up defence ties with key Asia-Pacific allies in a move sure to rile Beijing.

Ukraine has accused Russia of sending troops and weapons to help separatists in eastern Ukraine launch a new offensive.

Yesterday, British Prime Minister David Cameron blasted Russia's actions as unacceptable, warning that they could draw greater sanctions from the US and the European Union.

"If Russia takes a positive approach towards Ukraine's freedom and responsibility, we could see those sanctions removed; if Russia continues to make matters worse then we could see those sanctions increased; it's as simple as that," Cameron said.

Russia denies sending troops and tanks into Ukraine. But increasing violence, truce violations and reports of unmarked armed convoys travelling from the Russian border have aroused fears that a shaky September 5 truce could collapse.

Putin said the sanctions not only harmed Russia, but also the global economy. He said he would not bring up the issue at the Group of 20 meeting of leading developed and developing nations as "it'll make no sense".