Two massive explosions have rocked the Syrian capital Damascus with state media reporting dozens of people dead or injured.
The scale of the explosions is still unclear, but it has been suggested the explosions represent the deadliest attacks in the city for months.
The Syrian foreign ministry reported 55 people killed, 372 injured, and said the remains of 15 other unidentified people have also been found.
More than 1000 kilos of explosives were used, the foreign ministry spokesman said.
Residents said smoke was rising above buildings in the southern area of the capital, near to a major ring road and a military intelligence building, while state media blamed "terrorists" for the explosions.
The attacks will further endanger a fragile ceasefire brokered by international envoy Kofi Annan, during which activists claim several hundred people have been killed in attacks by both sides.
The Syrian government said that "dozens" of people had been killed in the near-simultaneous explosions on Thursday, and posted gruesome footage of burned bodies in the wrecks of cars and the shattered remains of victims.
The BBC said that the first blast attracted crowds to the site of the explosion, but that the second blast which exploded very nearby was the deadlier of the two.
Above: the rough location of the blasts which struck in the capital
Medical workers were reportedly collecting human remains from the road, according to the Associated Press - who have a reporter on the scene.
The AP also said that the facade of the nearby intelligence HQ had collapsed, but that the structure appeared secure.
Video posted online purported to have captured the sound of the second explosion. Residents who said they were on the scene reported via social media the shocking size of the blast:
Military intelligence buildings are said to be nearby to the massive crater site.
According to the AFP the head of the UN observer mission, Robert Mood, visited the site of the explosions, where he said they represented an act of "terrible violence".
"It is not going to solve any problems. It is only going to create more suffering for women and children," he said.
Samir Nashar, of the rebel Syrian National Council which is based in Turkey, claimed the regime "is behind this".
Nashar reportedly told AFP that the blasts were intended to send a warning to the UN.
A spokeswoman for the Revolution Council of Damascus has also aleged in an interview with the Guardian that an eyewitness to the attack was shot by a government sniper.
But on Twitter the foreign ministry spokesman called on the opposition to condemn the attacks:
No group has yet claimed official responsibility for the attacks.
The attacks are the first in the city since 27 April, when a blast killed 10 people near a mosque.
Earlier this week the rebel Free Syrian Army leader Riad al-Assad threatened to resume attacks on government troops after he claimed the government was not keeping its promises over the ceasefire.
Meanwhile residents in Homs reported sustained attacks by security forces overnight, with activists claiming a severe rise in the number of bombings.
On Wednesday a bomb in the city of Dara'a narrowly missed a convoy of UN observers, who are in the country to monitor the ceasefire brokered by international envoy Kofi Annan.
The London-based Syrian Network for Human Rights said that at least 23 people were killed on Wednesday, including 12 people in Homs.
After the blast on Wednesday UN secretary general Ban Ki-moon warned both sides there there was only a "brief window" to avoid a civil war.
"[There is only] a brief opportunity to create an opening for political engagement between the government and those seeking change," he said.
In December twin suicide car bombs killed 44 people in Damascus, and were condemned by the United Nations as "terrorist attacks".
More than 9,000 people have been killed in Syria since the start of the uprising in March 2011, the UN has said. The Syrian Observatory For Human Rights puts the total killed closer to 12,000.
Activists with The Local Co-ordination Committees group say that 1,000 people have been killed since the start of the ceasefire.