The attacks, which killed more than 50 people, came as the opposition umbrella group, the Syrian National Coalition, was meeting in Cairo to discuss proposals to hold conditional talks with President Bashar Al Assad's regime.
Damascus hit by its deadliest bombing in Syria war
DAMASCUS // A car bomb exploded close to ruling party offices in Damascus on Thursday, killing more than 50 people and causing widespread destruction in the capital's deadliest attack since Syria's civil war erupted.
The bombing, blamed on "terrorists" by both the regime and its opponents, rocked the city centre and sent thick smoke scudding across the skyline, shortly before a mortar attack on a nearby military headquarters.
The attacks came as the opposition umbrella group, the Syrian National Coalition, was meeting in Cairo to discuss proposals to hold conditional talks with President Bashar Al Assad's regime.
Images of charred bodies lying next to mangled vehicles were aired on state television, which said children were among those wounded as the blast was near a school in the central district of Mazraa.
Sirens rang out and machine-gun fire was heard as firemen rushed to the scene to douse the flames.
Police said the bomb exploded at 16 November Square near the ruling Baath party's head offices, and Russian news agencies reported the windows of Russia's embassy in Damascus were blown out, though none of its staff were hurt.
Syrian state media put the toll at 53 with more than 200 wounded.
The Britain-based activist group the Syrian Observatory for Human Rights, which compiles information from activists inside Syria, said at least 59 people were killed, including 16 members of the security forces. The rest were civilians, it said.
Previously, the deadliest explosion in Damascus was on May 10, 2012, when twin suicide bombings killed 55 people.
Witnesses at yesteday's blast said a car exploded at a security checkpoint between the Russian Embassy and the central headquarters of Assad's ruling party.
"It was huge. Everything in the shop turned upside down," a local resident told the Associated Press. He said three of his employees were injured by flying glass that killed a young girl who was walking by when the blast hit.
"I pulled her inside the shop but she was almost gone. We couldn't save her. She was hit in the stomach and head," he said.
Among those wounded by flying glass was Nayef Hawatmeh, the leader of the Democratic Front for the Liberation of Palestine, a radical Damascus-based Palestinian group.
An official at his office, about 500 metres from the bomb site, told the Associated Press Mr Hawatmeh was wounded in the hands and face. He was taken to hospital and later released.
There was no immediate claim of responsibility, but the foreign ministry blamed "terrorist groups linked to Al Qaeda". The Al Assad regime refers to rebels battling to oust the president as terrorists.
The opposition also denounced as "terrorists" those behind the bombing.
"Any acts targeting civilians with murder or human rights violations are criminal acts that must be condemned, regardless of the perpetrator or the justification," the National Coalition said on Facebook.
Within hours of the car bombing, two other bombs went off elsewhere in the city and a mortar attack struck the army's central command. Thirteen people were killed by the other two bombs, activists said.
The attacks come two days after two mortar shells exploded near the Tishreen presidential palace in Damascus, increasingly targeted in the past year by suicide bombings, some claimed by the Al Nusra Front Islamist group, including the May 10 attack last year.
They added urgency to the National Coalition meeting in Cairo, where discussions were centered on an offer by the opposition group's chief to hold direct talks with the regime.
"The agenda is long and among the issues to be discussed is the initiative of Ahmed Moaz Al Khatib," a delegate, Khaled Nasser, said.
Mr Al Khatib has offered to talk to regime officials without "blood on their hands" - an initiative welcomed by the Arab League and the United States as well as Mr Al Assad's allies Iran and Russia.
But the Syrian National Council, a key part of the coalition, has rejected any talks until Mr Al Assad quits, and the regime says it will only negotiate without pre-conditions.
The UN-Arab League peace envoy Lakhdar Brahimi, who on Wednesday extended his mission by six months, has urged support for the plan, saying talks would "be a start to exiting the dark tunnel".
The United Nations says at least 70,000 people have been killed in the conflict, and the violence frequently spills across Syria's borders, spiking already-simmering regional tensions.
On Wednesday, the rebel Free Syrian Army threatened to hit back at the Lebanese militant group Hizbollah, which backs Mr Al Assad, unless it stops shelling FSA-held territory from across the border.
Gen Selim Idriss, the FSA chief of staff, said the rebels were giving Hizbollah a 48-hour deadline to stop the attacks and "as soon as the ultimatum ends, we will start responding to the sources of fire".
* Agence France-Presse and Associated Press