The UN Security Council condemned the deadliest bomb attacks of Syria's 14-month uprising, urging all sides to stick to an international peace plan after at least 55 people were killed.
The Syrian government and opposition traded the blame for Thursday's twin suicide bomb attacks in Damascus, which also left nearly 400 people wounded in horrific scenes of carnage.
Opposition leader Burhan Ghalioun told reporters in Tokyo on Friday Syria's government is trying to destroy the UN-brokered peace plan.
"The regime is now trying to kill this (Kofi) Annan plan, and by a new technique which is terrorism," Ghalioun said.
Ghalioun was adamant the government was behind the attacks and accused the authorities of colluding with outside bodies.
"The regime has operated very closely with al-Qaeda," he told reporters, adding that the bombings marked a change in tactics.
"We have to notice the timing of these bombings, the bombings started almost as soon as the regime removed heavy forces from the cities, we think there is a connection," he said.
The blasts during the morning rush hour further clouded a UN-backed ceasefire brokered by special envoy Kofi Annan that has failed to take hold since it went into effect on April 12.
Syrian state television aired gruesome footage of the aftermath of the twin explosions in the neighbourhood of Qazzaz, blaming rebels seeking to topple President Bashar al-Assad's embattled regime.
The television showed images of a woman's charred hand on a steering wheel, her gold bracelets dangling from her blackened wrist. Other burnt and mangled bodies lay in the street amid the carcasses of smouldering vehicles and rubble.
Russia and China, which have stymied Western efforts to heap stronger condemnation on Assad's government, joined in a UN Security Council denunciation of the attacks.
The 15 Security Council members "condemned in the strongest terms the terrorist attacks" in the Syrian capital, according to a statement.
The council called on all sides to "immediately and comprehensively" implement the six-point peace plan of UN-Arab League envoy Annan, "in particular to cease all armed violence".
UN leader Ban Ki-moon reaffirmed a call for all sides to cease violence and "to distance themselves from indiscriminate bombings and other terrorist acts", his spokesman Martin Nesirky said.
Syria's UN envoy said British, French and Belgian nationals were among foreign fighters killed in the country's mounting conflict and that there was Al-Qaeda involvement.
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The ambassador, Bashar Jaafari, told the Security Council that on top of the Damascus blasts, an explosion in the city of Aleppo had left "several civilian victims and massive damage to private property".
Jaafari said 12 foreign fighters had been killed and 26 detained in recent clashes with Syrian forces, "including one French citizen, one British citizen, one Belgian citizen".
He said a list of the 26 foreigners detained had been sent to Ban and to the Security Council.
Jaafari renewed condemnation of Gulf Arab states and Turkey whom he accused of backing the foreign fighters and Syrian rebels.
Washington called the Damascus attacks "reprehensible" while Annan described them as "abhorrent". Russia and China separately called for a stop to the violence and urged all parties in Syria to cooperate with Annan's peace plan.
The explosions took place on a main freeway in the south of Damascus, in front of a nine-storey security complex whose facade was heavily damaged while nearby residential buildings collapsed.
"Is that the freedom you want? Students from schools and employees going to work are dead," shouted one man in the middle of the destruction.
The interior ministry said the suicide attackers used a tonne of explosives, killing at least 55 people and wounding 372.
It added that emergency workers filled 15 bags with body parts, and that the blasts also destroyed around 200 cars.
"These crimes show that Syria is targeted by a terrorist attack launched by organisations armed and funded by parties who proclaim their backing to terrorist crimes," the SANA news agency quoted the foreign ministry as saying.
But the opposition Syrian National Council accused Assad's regime of staging the bombings in a bid to undermine a UN observer mission and to persuade the international community that Damascus was battling "terrorists".
The SNC accused the regime of placing the bodies of people it had killed at the site of the bombings, to claim that they died in the blasts.
The Syrian Observatory for Human Rights, a Britain-based monitoring group, said the Damascus bombings targeted an intelligence base and killed 59 people, including civilians and security personnel.
The watchdog says that more than 12,000 people, mostly civilians, have been killed in Syria since the revolt broke out in March last year.
Thursday's attacks came a day after UN observers monitoring the ceasefire escaped unharmed when a roadside bomb exploded as they were visiting the flashpoint southern city of Daraa. Ten Syrian troops escorting them were hurt.