Two suicide bombs struck the heavily guarded Syrian army headquarters in the heart of Damascus on Wednesday, killing four guards and sparking a gunbattle between troops and rebels, state media said.
A rebel officer and a rights group said the audacious attack which also left 14 people wounded was an inside job, while an Islamist rebel group said five of its fighters including a suicide bomber died during the assault.
Iran's Press TV, meanwhile, said one of its correspondents, a Syrian, was killed by sniper fire and its Damascus bureau chief wounded as they reported from the scene.
The spectacular attack on the army's operations command centre came as the worsening bloodshed, which left as many as 217 dead on Tuesday, dominated proceedings at the UN General Assembly in New York.
"Armed terrorist groups with affiliations abroad this morning carried out a new act of terrorism by detonating a car bomb and another device on the edge of the general staff compound," an army statement said.
"All senior commanders and other officers are safe and sound, and none of them was wounded," the statement carried by state media said.
But state television, citing a military official, said four troops guarding the headquarters were killed, and 14 civilians and soldiers wounded.
The broadcaster showed video footage of a white van exploding beside the headquarters, and a second blast inside the compound. It said the bombings came 10 minutes apart.
"The initial investigation shows that these terrorist explosions around and inside the army headquarters were caused by two car bombs driven by suicide attackers," the military official said.
President Bashar al-Assad's regime has systematically blamed unrest and violence on foreign-backed terrorist gangs since the revolt erupted in March 2011.
The rebel Free Syrian Army's Military Council in Damascus said on its Facebook page that "the Free Syrian Army has struck the military headquarters in Damascus's Umayyad Square."
A rebel officer and the Syrian Observatory for Human Rights said it was an inside job, while an Islamist rebel group said its men carried out the attack. The claims were impossible to verify.
"The operation was carried out by several Free Syrian Army battalions working with an officer and his troops on the inside," said Ahmed al-Khatib, spokesman for the FSA's Military Council in Damascus.
Khatib confirmed the attack was staged with two car bombs, but denied they were driven by suicide attackers, which is not a tactic used by the FSA in the past.
"A few minutes after the attack, fighters broke into the HQ compound with machineguns and rocket-propelled grenades," said Khatib.
An Islamist rebel group, Tajamo Ansar al-Islam (Gathering of Partisans of Islam) also claimed responsibility. Five of its fighters, including a suicide bomber, were killed in the attack, the group said in an online statement.
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The group said bombs placed on the third floor of the building with the help of sympathisers within the military had been detonated.
It was the biggest attack on the security apparatus since a July 18 suicide bombing against a heavily guarded headquarters in Damascus killed four top regime officials, including defence minister General Daoud Rajha and Assad's brother-in-law, Assef Shawkat.
-- Iran media blames Turkey, Saudi Arabia, Qatar --
Iran's Press TV said its correspondent Maya Nasser was killed and its Damascus bureau chief Hussein Mortada, a Lebanese, was wounded at the army compound.
Press TV’s newsroom director, Hamid Reza Emadi, told AFP that Nasser, 33, was killed instantly when he was shot in the neck while reporting live.
"We hold Turkey, Saudi Arabia and Qatar responsible for the murder of our correspondent in Damascus, (as) they provide weapons to the insurgents in Syria and the insurgents are using sniper fire," Emadi said.
Early on Wednesday, pro-government militia executed at least 16 civilians in their homes in the Barzeh neighbourhood of north Damascus, according to the Observatory, which said the dead included six women and three children.
It said at least 132 people were killed nationwide on Wednesday, among them 83 civilians, in a toll which did not include the Press TV journalist.
A former FSA commander, meanwhile, told a Damascus conference of opposition groups tolerated by the regime he had decided to return to the regular army.
"The solution in Syria does not lie in the use of weapons or violence or explosions or the killing of innocents," said Captain Khaled Abdel Rahman al-Zamel, who was identified as FSA head in the south.
The opposition's foreign backers ramped up calls for Assad's exit at the General Assembly in New York, while the Observatory said that more than 30,000 people, mostly civilians, had been killed in 18 months of conflict.
Britain's Prime Minister David Cameron said the blood of children killed in Syria had become a "terrible stain" on the UN reputation.
"The blood of these young children is a terrible stain on the reputation of this United Nations," he said.
"And in particular, a stain on those who have failed to stand up to these atrocities and in some cases aided and abetted Assad's reign of terror."
He announced a new British $12 million donation to international humanitarian efforts and appealed for other countries to give more.
UN-Arab League peace envoy Lakhdar Brahimi has warned there will be no quick solution to the conflict.