Two suicide bombers killed at least 55 people and wounded nearly 400 in the Syrian capital Damascus on Thursday, authorities said, in the deadliest attacks of the country's 14-month uprising.
The blasts during the morning rush hour left an apocalyptic scene of destruction and further put into question a UN-backed ceasefire that has failed to take hold since it went into effect on April 12.
UN-Arab League envoy Kofi Annan, who brokered the truce, strongly condemned the bombings as the regime of President Bashar al-Assad and the opposition accused each other of being responsible.
Russia and China, both supporters of Assad's embattled regime, called for a stop to the violence and urged all parties in Syria to cooperate with Annan's peace plan.
State television aired gruesome footage of the aftermath of the twin explosions in the neighbourhood of Qazzaz, blaming "terrorists", the term used by authorities to refer to rebels seeking to topple Assad's 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.
"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 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.
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 of others who died, and that the blasts also destroyed around 200 cars.
The Syrian Observatory for Human Rights, a Britain-based monitoring group, said the bombings targeted an intelligence base and killed 59 people, including civilians and security personnel.
The 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.
"This is yet another example of the suffering brought upon the people of Syria," said Major General Robert Mood, chief of a UN observer mission, who visited the site of the explosions.
"We, the world community, are here with the Syrian people and I call on everyone within and outside Syria to help stop this violence," he added.
In Geneva, Annan said through his spokesman Ahmad Fawzi that he "condemns in the strongest possible terms the attacks that took place earlier today in Damascus."
"Any action that serves to escalate tensions and raise the level of violence can only be counter-productive to the interests of all parties," he added.
The opposition Syrian National Council accused Assad's regime of staging the bombings in a bid to undermine the UN observer mission and to impress upon the international community that the regime was battling "terrorists."
"This is the only way for the regime to claim that what is happening in Syria is the work of terrorist gangs and that Al-Qaeda is expanding its presence in Syria," said Samir Nashar, of the exile group's executive branch.
The European Union condemned the attacks which it described as "an act of pure terrorism."
Damascus has been the target of a number of bombs in the past few months.
Suicide bombers hit two security service bases in the capital on December 23, killing 44 people, in attacks the regime blamed on Al-Qaeda but which the opposition said were the work of the regime itself.
Commenting after Wednesday's Daraa attack, UN leader Ban Ki-moon warned of a "brief window" to avoid civil war and indicated the future of the ceasefire monitoring mission was in doubt.
Highlighting an "alarming upsurge" of roadside bombs, alongside government attacks, Ban said in New York that both sides "must realise that we have a brief window to stop the violence, a brief opportunity to create an opening for political engagement between the government and those seeking change."
He also warned that such bombings cast doubt on the future of the mission set up to monitor the month-old truce brokered by Annan.
If the violence did not stop, Ban said he feared "a full-scale civil war with catastrophic effects within Syria and across the region."
Elsewhere in the country on Thursday, at least 12 people were killed, including seven civilians, the Observatory said.
It said five intelligence officers died in a dawn car bombing in the northern city of Aleppo and a member of the security forces was also killed there by unidentified gunmen.
The watchdog says that more than 12,000 people, mostly civilians, have been killed in Syria since the revolt -- inspired by Arab Spring uprisings -- broke out in March last year.
More than 900 of them have died since the UN-backed truce was supposed to have taken effect on April 12.