British Prime Minister David Cameron and Russian President Vladimir Putin are expected to spar over Ukraine when they meet on the sidelines of the G20 summit in Australia, media reported Thursday.
Western governments, including Britain, have held Russia responsible for the fighting in Ukraine and have decried the Kremlin's alleged support to pro-Russian rebels in Ukraine.
Putin has been barred from the G8 summit representing the world's older developed economies, and since then, Cameron has repeatedly advocated tougher economic sanctions against Russia.
British officials described Cameron's scheduled bilateral meeting with Putin as a "brush-by", suggesting that it will be relatively short, The Guardian reported.
Putin had engineered a ceasefire in Ukraine before the NATO summit in September, but since then there has been continued fighting and a further decline in the Russian rouble.
NATO claimed to have noticed Russian military equipment and troops moving into eastern Ukraine this week, media reported.
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The troop activity follows recent elections in rebel-held parts of eastern Ukraine that the US and the EU consider illegitimate.
German Chancellor Angela Merkel reiterated that the EU was planning to add the winners of those elections to the existing sanctions lists, but said that no new economic sanctions were being planned.
EU's new foreign policy chief, Federica Mogherini, however, said that EU foreign ministers would consider increasing sanctions at a meeting next week.
Cameron has privately admitted that it was very difficult to be certain that Putin any longer told the truth to his fellow world leaders, but he would underline to Putin that he did not want to see a return to the Cold War period.
Australian Prime Minister Tony Abbott confronted Putin Tuesday in Beijing over Russia's alleged role in the downing of the Malaysia Airlines flight MH17 in Ukraine last July, and called for an apology and compensation from Russia.
Russia has, however, rejected Abbott's demands and had also sent its warships towards Australia ahead of this week's G20 summit in Brisbane in an apparent show of its muscle power.