A suicide bomber detonated an explosives-laden car outside security headquarters in Syria's biggest eastern city on Saturday, killing seven people and injuring 100, the government said.
The attack, the first of its kind in Deir Ezzor since an anti-regime uprising broke out in Syria in March last year, came as world powers discussed ways to end the relentless bloodshed.
"A car bomb exploded in the Ghazi Ayyash neighbourhood of Deir Ezzor," said state television, adding the attack was carried out by a "terrorist suicide bomber."
Foreign ministry spokesman Jihad Makdisi said on Twitter that there were seven "martyrs" and 100 injured in a "suicide explosion," which involved 500 kilos (1,100 pounds) of explosives.
However, state news agency SANA spoke of a "booby-trapped car."
The explosion went off on a road housing a military and air force intelligence headquarters, and a military hospital, said the Syrian Observatory for Human Rights.
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.
"Residential buildings and public and private installations near the site of the terrorist attack suffered serious damage," the television said.
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," a statement said.
"These repetitive blasts are part of the regime's plan to sow chaos and trouble, given that it failed to repress the revolution of the Syrian people."
Elsewhere, a rocket slammed into ruling Baath party 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 such attacks on "terrorists".
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 Thursday he believed al Qaeda committed the Damascus attack.
"Very alarmingly and surprisingly, a few days ago, there was a huge serious massive terrorist attack. I believe that there must be al Qaeda behind it."
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, 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. Some of the attacks we have seen clearly bear some of the terrorist hallmarks with which we are familiar from elsewhere."
The same day, 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.
On the ground, the Observatory said at least 14 people died in violence across the country on Friday as thousands took to the streets for an unprecedented anti-regime demonstration in Aleppo.
Protests demanding Assad's ouster also took place in Damascus, Deir Ezzor, northeastern Hasaka and Idlib, and Homs in central Syria, said the Observatory.
The Observatory said tens of thousands of people rallied across the country, in the biggest demonstrations since an April 12 ceasefire which has been violated on a daily basis.
With the violence 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 observers' 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.