Fierce fighting erupted between state forces and rebels in several parts of Syria on Thursday, activists said, including a town close to the capital Damascus, where an advance UN peacekeeping team was expected to arrive.

Explosions and heavy machinegun fire rocked Douma, just 12 kilometres (8 miles) from the seat of government, activists from the Revolutionary Council of the Damascus Countryside said.

They said columns of smoke were spiraling from several buildings.

Syria has been struggling to suppress a year-long revolt against President Bashar al-Assad's rule that has turned from a peaceful uprising to, at least partly, an armed insurgency.

The flare-up in violence comes ahead of the arrival of a United Nations advance team to Damascus, that will be trying to broker a deal to deploy observers to monitor a ceasefire plan agreed by the government.

The British-based Syrian Observatory for Human Rights said army reinforcements were being sent into Douma as fighting continued amid unconfirmed reports of civilian casualties.

In northern Aleppo province, close to the Turkish border, the Observatory said security forces were trying to storm two villages and had been fighting rebels for more than two hours.

"The loudspeakers at local mosques called for members of the regime army to defect and come into the towns," the group said, citing information from its network of activists inside Syria.

Four soldiers were killed and several civilians were reported wounded, it said.

In neighbouring Idlib province, a rebel was shot dead by snipers and three civilians were injured by random gunfire in the town of Khan Sheikhoun, it added.