International envoy Kofi Annan says he is "shocked and appalled" by reports of a mass killing in the Syrian village of Tremseh.

Syrian troops began pulling out today from some calm cities and headed back to their bases a week ahead of a deadline to implement an international ceasefire plan, a government official said.

Syria launched a long-anticipated assault to crush the opposition in the rebellious north today, bombarding its main city with tank shells from all sides and clashing with rebel fighters struggling to hold back an invasion.