The head of the dissident Free Syrian Army charged in remarks published Sunday that Al-Qaeda has links with the powerful airforce intelligence of the regime of President Bashar al-Assad.
"If Al-Qaeda militants have indeed entered the country, it happened with the cooperation of that agency," FSA chief, Colonel Riyadh al-Asaad, told Kuwait's Al-Rai newspaper.
He also held the Syrian regime responsible for Thursday's twin suicide bombings in Damascus that killed 55 people and wounded 372 and called for an international investigation.
"If the (US) information that Al-Qaeda had entered Syria is accurate, the regime alone is responsible for their entry. We know that the Al-Qaeda militants are linked to the Syrian airforce intelligence," Asaad said.
Asaad also denied claims by Damascus that jihadist and Salafi groups were active in Syria.
Al-Nusra Front, an Islamist group unknown before the Syrian revolt, released a video on Saturday claiming responsibility for the attacks as revenge for regime bombing of residential areas in several parts of the country.
But claims by the group, including for past bombings, have been hard to verify.
The main opposition coalition, the Syrian National Council, has accused the authorities of resorting to "terrorism" itself in a bid to torpedo a peace plan drafted by UN and Arab League envoy Kofi Annan.
Asaad stressed that the FSA has so far complied with the plan whereas the regime has committed scores of violations. He said he believes the plan has failed and called for not taking a long time to announce its failure.