Twin blasts hit the heart of Damascus on Saturday, killing at least 27 people in an attack on security installations that state television blamed on "terrorists" seeking to oust President Bashar Al-Assad.
Syrian television reported that cars packed with explosives had targeted an intelligence centre and a police headquarters at 7:30am (0530 GMT), blowing the front off one building and sending debris and shattered glass flying through the streets.
Gruesome images from the sites showed what appeared to be smouldering bodies in two separate vehicles, a wrecked minivan smeared with blood, and severed limbs collected in sacks.
At least 27 people were killed and 97 were wounded, another television channel said, quoting Health Minister Wael Al-Halki.
"We heard a huge explosion. At that moment the doors in our house were blown out ... even though we were some distance from the blast," one elderly man, with a bandage wrapped round his head, told a public television channel.
No one claimed responsibility for the coordinated detonations, which echoed similar attacks that have struck Damascus and Syria's second city Aleppo since December.
The explosions came just two days after the first anniversary of the uprising, in which more than 8,000 people have been killed and about 230,000 forced to flee their homes, according to United Nations figures.
They also coincided with a joint mission by the Syrian government, the United Nations and the Organisation of Islamic Cooperation that was due to start assessing humanitarian needs in towns across Syria, which have suffered from months of unrest.
One source involved in the mission said team members were still gathering in Syria and it was not immediately clear if they would begin their work this weekend as previously planned.
The UN-Arab League envoy for Syria, Kofi Annan, warned on Friday that the crisis could spill over into other neighbouring countries and urged international powers to lay aside their differences and back his peace initiative.
While the West and much of the Arab world have lined up to demand that Assad steps down, his allies Russia, China and Iran have defended him and cautioned against outside interference.
"The stronger and more unified your message, the better chance we have of shifting the dynamics of the conflict," an envoy said, summarizing Annan's remarks to a closed-door meeting of the 15-nation Security Council.
Turkey said on Friday it might set up a "buffer zone" inside Syria to protect refugees fleeing Assad's forces, raising the prospect of foreign intervention in the revolt, although Ankara made clear it would not move without international backing.
Television showed numerous men and women receiving hospital treatment for multiple wounds following Saturday's strikes. Syria's Sana news agency said the blasts had hit the criminal police force headquarters and the Air Security Directorate.
The attacks followed three suicide bombings in Damascus in December and January, which killed at least 70 people, and an attack in Aleppo in February that killed 28.
Al-Qaeda leader Ayman Al-Zawahri, in a video recording posted on the Internet last month, urged Muslims around the region to help Syrian rebels.
Syria has previously blamed Al-Qaeda for at least some attacks on its territory and vowed to respond with an iron fist.
The army has shelled rebel strongholds in various places in recent weeks before sending in troops to round up suspects. Opposition activists say thousands of civilians have died, with many bodies found bearing signs of torture.
The Syrian government denies accusations of brutality and says it is grappling with a foreign-backed insurgency.
Diplomats have warned that without a swift resolution, Syria will descend into a full-blown civil war.
Syria lies in a pivotal position within the Middle East, bordering Turkey, Jordan, Israel, Iraq and Lebanon, and its 23-million-strong population comprises a mix of faiths, sects and ethnic groups.
"I think that we need to handle the situation in Syria very, very carefully," Annan told reporters in Geneva on Friday.
"Yes, we tend to focus on Syria but any miscalculation that leads to major escalation will have impact in the region which would be extremely difficult to manage," he said.
The veteran diplomat presented Assad with a six-point peace proposal at talks in Damascus last weekend. Envoys said he told New York on Friday that the response to date was disappointing.
Assad insists the Syrian opposition stops fighting first, while the United States, Gulf Arabs and Europeans have demanded that Assad and his much stronger forces must make the first move. Russia wants both sides to stop shooting simultaneously.
Annan will send a team to Damascus early next week to discuss a proposal to deploy international monitors in the country, his spokesman Ahmad Fawzi has said.
Increasingly alarmed by the growing violence, Turkey urged its citizens to quit Syria on Friday and raised the prospect of creating a safe zone on its border to protect the refugees.
"A buffer zone, a security zone, are things being studied," Turkish Prime Minister Tayyip Erdogan told reporters, adding this was not the only proposal under consideration.
Ankara is wary of military intervention and has made clear any creation of a 'security zone' would need some form of international agreement, not least because it would require armed protection and could alter the dynamics of the uprising.
Turkey says it is now hosting 14,700 Syrian refugees after 250 people crossed its borders on Friday. Some 1,000 had arrived the day before, fleeing fierce fighting in Idlib province.