DARAA: A roadside bomb wounded six soldiers as they escorted a convoy of UN peace observers, including the general who heads the mission, in southern Syria on Wednesday, an AFP photographer said.

The explosive device, which appeared to have been planted underground, detonated as the convoy of four vehicles was about to enter the town of Daraa, cradle of a 14-month uprising against President Bashar al-Assad's regime.

Major General Robert Mood of Norway, the head of the UN mission, was in the convoy but escaped unharmed along with 11 other observers and his spokesman Neeraj Singh, said the photographer who was travelling in the convoy.

The bomb attack was the latest breach of a month-old ceasefire agreement that international envoy Kofi Annan said could be the last chance to avert a civil war in Syria.

Troops elsewhere pounded a rebel hideout near the capital Damascus, said the Syrian Observatory for Human Rights.

The shelling of Douma, about 13 kilometres northeast of the capital, came as violence across Syria killed at least three people, said the Britain-based watchdog.

Forces loyal to Assad lost two of their own men in clashes with rebel fighters in the eastern province of Deir Ezzor, said the Observatory.

On Tuesday, Annan told the UN Security Council the priority in Syria was “to stop the killing,” and expressed concern that torture, mass arrests and other human rights violations were intensifying.

Regime forces “continue to press against the population,” despite a putative truce that started on April 12, but attacks are more discreet because of the presence of the UN military observers, diplomats quoted him as saying.

“The biggest priority, first of all we need to stop the killing,” Annan told reporters in Geneva, adding that his six-point peace plan is “the only remaining chance to stabilise the country.”

Annan briefed the council on his efforts to get Assad to implement the plan, which he said was possibly “the last chance to avoid civil war.” He stressed, however, that the peace bid was not an “open-ended”opportunity for Assad, the diplomats who attended the briefing said.

Annan plans to return to Damascus in the coming weeks, his spokesman said Tuesday, though this depended on events on the ground there. It would be only his second visit since his mission began earlier this year.

US ambassador to the UN Susan Rice said Washington's goal was still the removal of Assad.

“The United States remains focused on increasing the pressure on the Assad regime and on Assad himself to step down,” Rice said.

“The situation in Syria remains dire, especially for the millions who continue to endure daily attacks and are in urgent need of humanitarian assistance,” she told reporters after Annan's briefing.

Top US officials are to meet delegates from the Syrian Kurdish National Council (KNC) in Washington this week to try to build a “more cohesive opposition” to Assad, a State Department spokesman said.