More Arab League observers are due to arrive in Syria as part of a deal with Damascus to try to end months of violence gripping the country.
The main opposition group urged them to go immediately to the central city of Homs, which is reportedly besieged by government forces.
Activists say a number of people have been killed in the town by mortar shelling and machine-gun fire.
Damascus says it is fighting armed gangs intent on destabilising Syria.
The United Nations says more than 5000 people have been killed across the country since protests against the government of President Bashar al-Assad erupted in March.
The BBC reports that such claims are hard to verify as most foreign media are banned from reporting in Syria.
The observer mission will eventually have up to 200 members, and it plans to meet both government officials and the opposition.
