A suicide bomber detonated an explosives-laden car outside security headquarters in Syria's biggest eastern city on Saturday, killing nine people and wounding 100, state media said.

The attack was the the first of its kind in Deir Ezzor since an anti-regime uprising broke out in Syria in March 2011, and the deaths there came as at least another 10 people died elsewhere in the country.

Among the dead were a woman and her two children gunned down in the norther city of Aleppo, said the Syrian Observatory for Human Rights.

A "terrorist suicide bomber" used 1,000 kilograms (2,200 pounds) of explosives in the attack on the Deir Ezzor neighbourhood of Ghazi Ayyash, said state television.

The powerful explosion left a crater 3.5 metres (yards) deep and damaged buildings within a radius of 100 metres, the channel said, adding that a four-year-old girl was among those critically wounded.

It occurred on a road housing a military and air force intelligence headquarters and a military hospital, according to the Observatory.

Images broadcast on state television showed a large bloodstain on the ground, a damaged building and vehicles charred by the blast, as well as smoke rising from the targeted district.

There was no claim of responsibility for the bombing but, as typically happens in such cases, the opposition blamed it on the regime of President Bashar al-Assad.

"The Syrian National Council places on the Syrian regime the entire responsibility... for the criminal bombings in several Syrian cities, including the one today in Deir Ezzor," it said in a statement.

Elsewhere, a rocket slammed into the ruling Baath party's offices in northern Aleppo province, the Observatory said, a day after unprecedented anti-regime protests in the provincial capital of the same name.

"Unidentified gunmen targeted a Baath party office in Aleppo's Al-Bab town with a rocket-propelled grenade," said the Britain-based watchdog.

Immediately after the attack, clashes broke out between the gunmen and guards, but there were no reports of any casualties.

The government said it had foiled a suicide bomb attack in Aleppo on May 11, a day after twin bombings in Damascus killed 55 people and wounded nearly 400. It has repeatedly blamed bomb attacks on "terrorists" and Al-Qaeda.

In Homs, sniper fire killed a civilian and blasts were heard as shells rained down on the flashpoint central city, the Observatory said.

Saturday's bombing in Deir Ezzor came a day after regime forces foiled a would-be car bombing in the same city, which is about 110 kilometres (70 miles) from the Iraqi border.

What started out as a popular uprising has over time developed into an increasingly militarised revolt, after Assad's regime used force to crack down on peaceful protests.

UN chief Ban Ki-moon said on Thursday he believed Al-Qaeda committed the Damascus attack.

On Friday, UN spokesman Martin Nesirky said there was no hard proof of that, but that the "Damascus attacks were clearly carried out by a group with organisation and intent."

Assad, as well as the United States and Russia, has already pointed to an Al-Qaeda presence in Syria since the revolt began.

On Friday, G8 leaders met for dinner at Camp David, outside Washington, with discussions focused heavily on the bloodshed in Syria and Iran's contested nuclear programme.

According to a senior US official, there was broad agreement on the need for political transition in Syria.

Saturday's violence came a day after at least 14 people were killed across the country as thousands took to the streets for an unprecedented anti-regime demonstration in Aleppo, as well as elsewhere.

With the killing unabated, UN-Arab League envoy Kofi Annan plans to return to Damascus soon to further efforts to find a peaceful solution to the crisis, his spokesman said on Friday, without saying when.

The head of the UN observer mission, Major General Robert Mood, told reporters in Damascus his mission "will reach full operational capabilities in record time."

But he acknowledged that "no volume of observers can achieve a progressive drop and a permanent end to the violence if the commitment to give dialogue a chance is not genuine from all internal and external factors".

According to the Observatory, more than 12,000 people have been killed in Syria since the revolt broke out in March last year, most of them civilians.