Russian Foreign Minister Sergei Lavrov on Friday met his Syrian counterpart Walid al-Muallem, urging Damascus to do more to implement the plan of peace envoy Kofi Annan. Lavrov met Muallem for two hours of previously unannounced talks in Russia\'s second city of Saint Petersburg as global concern grows over the violence in Syria between the regime of President Bashar Assad and rebels. \"We called on them (the Syrian regime) to back up their declarations about readiness to implement the Kofi Annan plan with deeds,\" Lavrov told state television after the meeting. \"They have already done a lot but they can and must do much more.\" Lavrov said that Muallem had promised him in the name of Assad that the Syrian government was ready for a \"synchronised\" withdrawal of troops from Syrian towns as long as the rebel opposition did the same. \"The minister assured me of this today,\" he said. Acknowledging the gravity of the Syrian crisis which has already left more than 15,000 dead and raised fears over the viability of the Annan plan, Lavrov said: \"Now we are in a quite acute phase of the crisis.\" Assad\'s Western and Arab foes, who have repeatedly called on Moscow to halt all backing for the Syrian regime as well as military cooperation, have been particularly concerned by a Russian attempt to deliver helicopters to Syria. The cargo ship Alaed, which was forced to turn back from British waters this week, was carrying attack helicopters bound for Syria that Russia had repaired for Assad\'s regime. But Lavrov said he felt no need to justify Russia\'s behaviour to the United States, ahead of a meeting with Secretary of State Hillary Clinton in Saint Petersburg next week. \"If my colleague asks about this question then I will answer but we do not intend to justify ourselves,\" he said. \"They cannot accuse us of anything because we are not violating any rules -- neither international law, nor U.N. Security Council resolutions nor our national law on export control which is one of the toughest in the world,\" he said.