BEIRUT  - Fierce clashes between rebel troops and Syrian forces rocked a Damascus district bristling with security facilities on Monday, just hours before experts sent by peace envoy Kofi Annan arrived in the capital.

The fighting, the heaviest in Damascus since a revolt against President Bashar al-Assad's regime erupted a year ago, came as the capital was still reeling from deadly weekend bombings.

State television said three "terrorists" and a security force member were killed in the clashes that erupted early morning in the upscale and heavily guarded Mazzeh neighbourhood of Damascus, where several security facilities are housed.

It said several people were also wounded on both sides.

Rami Abdel Rahman, head of the Syrian Observatory for Human Rights, said at least 18 security troops were wounded in the fighting that broke out before dawn in Mazzeh.

"The clashes were the strongest and the closest to security installations in the capital since the outbreak of the revolt a year ago," Abdel Rahman told AFP. He said that by 4:00 am (0200 GMT) the fighting had ebbed. Mourtada Rasheed, an activist in Damascus, said blasts and heavy shooting could be heard in Mazzeh as well as two other districts, Qaboon and Arbeen. "We woke up at 3:00 am (0100 GMT) to the sound of heavy machinegun fire and rocket propelled grenades (RPG)," said one resident of Qaboon who did not wish to be identified.

A resident of Mazzeh, located near the presidential palace and home to several embassies, said locals were terrified by the sound of gunfire.

"We were very scared but now the roads are clear and stores are open for business," she told AFP. Rasheed said the fighting was the result of a hit-and-run operation launched in Mazzeh by the rebel Free Syrian Army to ease pressure on other regions targeted by regime forces.

Violence was also reported on Monday in the central province of Hama, where several houses in the town of Qalaat al-Madiq were destroyed in shelling by security forces, the Britain-based Observatory said.

It added that troops also besieged and stormed the town of Kafar Shams, in the southern province of Daraa.

Monday's clashes came after twin car bombs ripped through two neighbourhoods of Damascus on Saturday killing 27 people according to the Syrian interior ministry. Another car bomb exploded on Sunday in a residential neighbourhood of Aleppo, Syria's second city and commercial hub, killing two people.

Assad enjoys a strong support base in Damascus and Aleppo, both of which had so far been largely spared the unrest shaking the country since the revolt against the regime began last March. More than 9,100 people have been killed in the fierce government crackdown to crush the uprising, according to the Observatory.

The regime has consistently blamed the unrest on foreign-backed "armed terrorist gangs" and has pressed its crackdown despite a chorus of international condemnation. On the diplomatic front, a mission sent by UN-Arab League special envoy Kofi Annan arrived in Damascus for talks on a monitoring operation to end the bloodshed.

"The mission has arrived. There are five people with expertise in political, peacekeeping and mediation," Ahmad Fawzi, spokesman for Annan, told AFP.

"They will be staying for as long as they are making progress on reaching agreement on practical steps to implement Mr Annan's proposals," he added.

Technical experts from the UN and Organisation of Islamic Cooperation were on Monday also working in Syria to assess the humanitarian impact of the regime's deadly crackdown on the protests.

"The joint OIC-UN mission entered Syria on Friday to carry out an evaluation of humanitarian aid," on a mission led by the Syrian government, OIC assistant secretary general Atta al-Mannan Bakhit told AFP.

The mission, with three OIC experts in the team, would cover 15 cities, he added. It would submit a report to the Saudi-based Islamic grouping and the United Nations on the humanitarian needs of the Syrian population.

In parallel with the mission, Jakob Kellenberger, president of the International Committee of the Red Cross, flew to Moscow for talks Monday with Russian Foreign Minister Sergei Lavrov on the "extremely difficult" humanitarian situation in Syria's protest centres.

"A daily ceasefire of at least two hours is imperative to allow the evacuation of the wounded," he said ahead of the mission to Moscow, an ally of Damascus which is seen as having some influence on Syria's leadership.