Syrian forces have shot dead 31 people in the last 48 hours during demonstrations in a northwestern town, residents said.

Official media said gunmen killed four policemen in the same town.

Protests against President Bashar al-Assad have grown despite reform gestures dismissed by the opposition and a continuing crackdown that has killed at least 1,100 people since the uprising erupted two months ago.

Residents said the killings in the northwestern town of Jisr al-Shughour began when snipers on the roof of the main post office fired at a funeral for six protestors killed during a demonstration on Friday.

The official news agency said 'armed terrorist groups' killed four police and attacked public buildings including the post office.

The Syrian Observatory for Human Rights said 31 civilians and four police died in Jisr al-Shughour.

Authorities have prevented most international media from operating in Syria, making it impossible to verify accounts of the violence.

In the eastern city of Deir al-Zor, centre of an oil producing area, residents said security forces killed two protesters after mourners set ablaze two buildings belonging to Assad's Baath Party, which has ruled Syria since it seized power in 1963.

Overnight, forces had fired at thousands of protestors in the city and injured scores as they tried to reach a main square to topple a statue of late President Hafez al-Assad, Bashar's father.

Night demonstrations have been held daily across Syria to circumvent the heavy security presence, though protests reach a peak after Friday midday prayers.

Human rights campaigners say security forces shot dead at least 70 protestors in the city of Hama on Friday.

But central neighbourhoods in Damascus and most of Syria's second city Aleppo have remained largely quiet as authorities tighten security in the two cities.