David Cameron is urging Vladimir Putin to make sure that 30 Greenpeace activists imprisoned in Russia can come home.
The British Prime Minister has called the charges against the activists "excessive" and has urged the Russian President to "de-escalate" the situation.
The 30 activists, including New Zealanders David Haussmann and Jonathan Beauchamp, have been charged with hooliganism by the Russian authorities after their ship, the Arctic Sunrise, was seized.
They were initially charged with piracy, although it was later changed to hooliganism, which carries a lesser sentence.
Cameron spoke to Putin this week and told him that they were "protesters rather than hooligans", his official spokesman said.