Syrian Foreign Minister Walid Mouallem said Tuesday that a cease fire should coincide with the arrival of international observers. Speaking after a meeting with Russian Foreign Minister Sergei Lavrov in Moscow, Mouallem said that Syria has withdrawn some troops from some provinces in accordance with UN-Arab League envoy Kofi Annan's ceasefire plan, although accused opposition groups in the country of escalating the violence. He said Syria had asked Annan to open contacts with opposition groups and countries supporting them, and to report back to Damascus with their response. While welcoming the idea of international observers, Mouallem said Syria wants to take part in their selection and to ensure they work under the auspices of Syrian sovereignty.Syrian tanks shelled the central city of Hama in the early hours of Tuesday morning, an activist said, and tanks continued to patrol the streets on the day Syrian President Bashar Assad has agreed to start withdrawing government forces from urban areas."At 2 a.m. we heard two shells fall and the sound of tanks moving around the streets," said Manhal Abu Bakr, an activist and citizen journalist."There is no gunfire now. They shell us at night so that it is hard to film," he said over Skype. Internet video footage, which Abu Bakr said was filmed in Hama overnight, showed nighttime explosions in a built-up area.In Douma, a suburb of the capital Damascus, another activist said tanks were still in the streets on Tuesday morning.Diplomats trying to contain a crisis that has inflamed the Middle East and pitched old Cold War rivals into opposing camps will not wish to abandon their most comprehensive peace plan yet. The plan's author, international envoy Kofi Annan, visits Turkey and Iran on Tuesday, while Russia hosts the Syrian foreign minister.