Syrian army defectors attacked a military intelligence base today in one of the most daring raids in eight months of unrest as the Arab League chief said everything must be done to end the violence.

The early-morning raid on the air force intelligence base just outside Damascus was among the most spectacular carried out by the growing number of deserters from Assad's largely conscript armed forces who have refused orders to open fire on civilian protesters.

The unprecedented movement against Assad's 11-year rule has been spearheaded by peaceful demonstrators but, in recent months, deserters have organised themselves into a Free Syrian Army that has inflicted growing losses on the regular armed forces.

"The Free Army struck with rockets and RPGs (rocket-propelled grenades) the headquarters of air force intelligence which is located at the entrance of Damascus," said the Local Coordination Committees, an activist network, adding smoke was rising from the area.

There was no immediate word on casualties.

The activists, who illustrated the three-pronged attack in a plan attached to their statement, said prisoners held at the intelligence branch "were well" but the operation failed to secure their release.

The Free Syrian Army announced it was forming a temporary military council to spearhead the fight to oust Assad's regime.

The council aims to "bring down the current regime, protect Syrian civilians from its oppression, protect private and public property and prevent chaos and acts of revenge when it falls," it said in a statement received in Nicosia.

Colonel Riyadh al-Asaad, who defected from the regular army to form the Syrian Free Army in July, will chair the council.

In Hama, a flashpoint central province, security forces shot dead three army defectors and a civilian in the rural town of Keferzita, the Syrian Observatory for Human Rights said.

"Eight troops were killed and dozens other wounded on Wednesday morning when defectors attacked a military checkpoint in Keferzita," it added.

In Homs, another protest city further south, four civilians were killed by gunfire coming from a checkpoint, added the Britain-based watchdog, which also reported the deaths of a missing person and of a civilian who succumbed to wounds.

In the southern province of Daraa, cradle of the revolt, security forces killed a civilian at a checkpoint in the town of Hara, the Observatory added.

The violence came as Arab foreign ministers gathered in the Moroccan capital to ramp up the pressure on the Damascus authorities to honour the terms of an Arab League peace deal they signed up to on November 2.

Foreign ministers already agreed at a meeting in Cairo on Saturday to withdraw ambassadors from Damascus, impose political and economic sanctions and open talks with opposition groups on their vision for a post-Assad Syria.

The peace blueprint called for the protection of civilians, the withdrawal of troops from towns and villages where there have been clashes, the release of those detained during the protests and the launch of negotiations with the opposition.

Speaking on the sidelines of the Rabat meeting, Arab League Secretary General Nabil al-Arabi said "everything must be done to stop the ongoing bloodshed in Syria."

Arabi said he hoped Arab moves to send observers to Syria, where the United Nations estimates that more than 3,500 have died in the crackdown, would bear fruit within days.

But he reiterated no observers would be sent before a clear agreement is signed between the Arab League and Damascus, which failed to implement the earlier deal.

On Sunday, Syria said it would welcome the dispatch of an "Arab ministerial delegation accompanied by observers, civilian and military experts and Arab media."

It said the delegation would be able to see for itself the situation on the ground "and supervise, in coordination with the Syrian government, the application of the Arab (peace) plan."

Human rights groups say the regime has instead intensified its crackdown, with more than 70 people dying on Monday alone in one of the bloodiest days of the unrest.

On Tuesday, Syria freed more than 1,000 prisoners in an apparent 11th-hour bid to placate Arab leaders ahead of the Rabat meeting, at which it will not be represented.

Turkish Foreign Minister Ahmet Davutoglu warned a heavy price would be exacted on Assad's regime if it failed to halt the crackdown.

"The cost for the Syrian administration of not fulfilling the promises it made to the Arab League (to end violence) is its isolation in the Arab world as well," Davutoglu told his Arab counterparts in Rabat.

Yesterday, Ankara hit Syria with energy sanctions, halting joint oil exploration and threatening to cut power supplies to its southern neighbour, in moves strongly welcomed by Washington.