The rebel incursion close to the Assad regime's security directorate follows three fatal car bombings at the weekend outside security bureaus in two suburbs of Damascus, and in Allepo, Syria's second major city, where Assad also draws political support.

Residents in Mazzeh, a western district, said they were awoken before dawn on Monday by heavy machine gun fire that lasted two hours.

A pro-government TV station Ikhbariyah said three rebels and one security force member had been killed. Other unverified reports put the toll far higher.

Sources said Assad's security forces with tanks later searched for attackers, said to be members of the Free Syria Army, across Mezzah, which houses several foreign offices, including a Swiss embassy and government installations.

The Britain-based Syrian Observatory for Human Rights, which has activists throughout Syria, described the Mezzah attack as the "closest to security centers in Damascus" since the start of Syria's uprising a year ago.

Monday's clash follows government offensives in recent weeks on the central city of Homs, which prompted an international outcry over the fate of civilians, and in Syria's northern region of Idlib, near Turkey.

UN advance team arrives

A five-member technical team sent by Kofi Annan has arrived in Damascus. Its spokesman Ahmad Fawzi said the timing of Annan's next visit would "depend largely on progress being made by the Syrians in working with the mission."

The five had expertise in political mediation and peacekeeping, Fawzi added. The Organisation of Islamic Cooperation (OIC), which has experts with the mission, said it would observe the "overall humanitarian situation."

More generals defect, says Turkey

Turkey, which fell out with Assad months ago, has reportedly claimed the defection of two more Syrian generals. The French news agency AFP quoted a Turkish diplomat on the condition of anonymity as saying the pair had linked up with rebels.

That would raise to nine the total number of generals who have defected from Assad's regime over the past year.

In addition, 200 more Syrian refugees, including women and children, had crossed into Turkey, raising refugee numbers to more than 16,000, it said.

Red Cross chief visits Moscow

Visiting Moscow, the head of the International Red Cross (ICRC), Jakob Kellenberger warned the humanitarian situation in Syria was likely to get worse.

Entering talks with Russian Foreign Minister Sergei Lavrov, Kellenberger reiterated ICRC calls for a daily two-hour ceasefires in Syrian flashpoints.

More access by the ICRC and Syrian Arab Red Crescent was "essential," he said, to reach vulnerable civilians and make evacuations.

Russian naval base bolstered

Russian supply and reconnaissance ships stationed at the Syrian port of Tartus have been joined by a Russian naval tanker, according to the Interfax news agency.

It cited Russian fleet officials as saying Russia, which is a major arms supplier to Assad's regime, was maintaining its leased facilities in the Mediterranean port to demonstrate Kremlin concern over Syria's stability.

At the weekend, Lavrov came out in support of Annan's mediation efforts, saying "the Syrian government should quickly, without delay, support [Annan's] approaches."

"I repeat, we do not support the Syrian government. We support the need to start a political process. To do that it is first necessary to cease fire," Lavrov said.

ipj/mz (dpa, AFP, Reuters, AP)