Russia has called for the swift implementation of a ceasefire in the Gaza Strip following Israel's ground offensive under way since late Saturday, Russian media reported Sunday, according to dpa. Moscow was seriously concerned about the situation, President Dmitry Medvedev told Israel's caretaker Prime Minister Ehud Olmert on the telephone on Sunday, according to the Itar-Tass news agency said. The two leaders again emphasized the importance of the planned meeting of the so-called Middle East Quartet in Moscow, the report said. No date has been given for the meeting. Russian Foreign Minister Sergei Lavrov on Sunday called on both sides to end the bloodshed and the suffering of civilians.