Government forces and rebels, meanwhile, kept up the battle for the northern city of Aleppo.

The broadcaster said at least four people were killed in the Qamishli blast, while the Syrian Observatory for Human Rights said eight members of the security forces were killed and that the attack targeted their headquarters in the city.

"A suicide terrorist using a car laden with explosives attacked the western district of Qamishli," the television said.

The Britain-based Observatory said "at least eight members of the security forces were killed, and 15 were injured," adding that the blast was followed by heavy gunfire.

Amateur video uploaded on YouTube by activists showed a cloud of thick smoke rising over buildings in the city.

The Qamishli attack comes less than a week after a twin bomb attack struck the heavily guarded Syrian army headquarters in the heart of Damascus, killing at least four of its guards. An Islamist rebel group claimed the Damascus attack.

Sunday's bombing was the first time since the outbreak of the anti-regime revolt that Qamishli witnessed such a violent attack, Observatory director Rami Abdel Rahman said.

"The earth shook beneath us, the force of the explosion was immense," an activist who identified himself as Serdar told AFP via the Internet.

Abdel Rahman said the military pulled out of Kurdish regions in northeastern Syria, including Qamishli, several months ago and the rebel Free Syrian Army (FSA) had no presence in the city, although some other fighters are based there.

The Qamishli blast came as intense fighting swept Syria's second city Aleppo after a night of heavy shelling that destroyed houses and killed at least three people including two civilians, said the Observatory.

Aleppo has been the main battleground for the past two months of the country's 18-month conflict, and it has been gripped by fighting on an unprecedented scale since Thursday.

A group which relies on a network of activists on the ground said that rebel mortar fire damaged two helicopters at the Al-Nairab military airport in Aleppo.

The army, for its part, shelled several other districts of Aleppo and battled rebels in Aleppo's northern district of Jandul, the Observatory said.

"There were many rebels and soldiers killed, but both sides are trying to conceal their casualties," Abdel Rahman told AFP.

In Damascus province, rebels killed nine soldiers when they attacked a military checkpoint on the road linking the capital with Qatana to the southwest, the Observatory reported.

The monitoring group's death toll for Sunday before the Qamishli attack was at least 23 people killed -- 13 troops, five civilians and five rebels.

-- Envoy representative meets rebel --

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UN spokesman Khaled al-Masri told AFP, meanwhile, that Mokhtar Lamani, the head of UN-Arab League peace envoy Lakhdar Brahimi's office in Syria, met with an FSA commander in central Syria.

Lamani held talks with Colonel Kassem Saadeddine in the town of Talbisseh, Homs province, and other members of the FSA, which is made up of army deserters and civilians who have taken up arms against President Bashar al-Assad's regime.

The official also met with the governor of Homs province, Ghassan Abdelaal, as well as representatives of the International Committee of the Red Cross and Syrian Red Crescent.

Separately, Iraq's Foreign Minister Hoshyar Zebari vowed his country would stop and search any flights from top Damascus ally Iran over its territory suspected of carrying weapons to Syria.

"We have assured US officials that the Iraqi government is determined to land (Iranian) flights and carry out random searches," Zebari said, quoted by Arabic daily Al-Hayat.

Last week, US Secretary of State Hillary Clinton pushed Baghdad to deliver on pledges to stop such flights during a meeting with Iraqi Vice President Kudayr al-Khuzaie.

Zebari said the flights first started in March and were stopped after the Iraqis called on the Iranians to do so. By late July, however, the flights resumed.

"They (the Iranians) said they were not carrying weapons or ammunition but pilgrims, visitors and other things," said Zebari, adding that "just to be sure, we will land these planes."

Violence across Syria killed 118 people on Saturday -- 48 civilians, 41 soldiers and 29 rebels, the Observatory said, adding to its toll of over 30,000 killed since the uprising erupted in March 2011.

In its most recent estimate, the United Nations has put the overall toll from the conflict at more than 20,000 dead.

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