Two car bomb attacks in Damascus yesterday led to immediate accusations and recriminations between the government and opposition activists yesterday after Bashar al-Assad's regime seized upon the attacks as proof that it was facing an organised terrorist campaign involving al-Qa'ida.

More than 40 people were killed and 150 were injured in the two blasts, which came within minutes of each other and are the first large-scale suicide bombings of the Arab Spring.

As the government pointed the finger of blame at terrorists, the opposition countered that the explosions had taken place at a highly opportune time for the regime – just after the arrival of a team of observers from the Arab League to the Syrian capital.

Colonel Muammar Gaddafi had repeatedly claimed Libya's revolution was driven by al-Qa'ida and its allies.

Holding up the supposed threat of Islamist terror has been a common trait among dictators trying to cling to power during the popular revolts in North Africa and the Middle East.

Although senior figures in Syria's protest movement stopped short of directly accusing the regime of being responsible for the two bombs, many activists are convinced this is the case.

Some residents in Damascus claimed roads near the scene of the attacks in the Kafar Sousah district were shut off before the explosions took place.

A Foreign Ministry spokesman maintained the regime had received information about an impending attack.

"The Lebanese authorities warned us two days ago that an al-Qa'ida group infiltrated to Syria from [the northern Lebanese town of] Ersal," he said.

"Today's suicide bombers have caused many deaths. Freedom seekers should know that this is not the way to achieve democracy."

The Arab League delegation was taken to the blast site. There, pointing out a gouged-out crater, deputy foreign minister Faysel Mekdad said: "We said it from the beginning, didn't we? This is terrorism. They are killing the army and ordinary people."

Standing beside him, the head of an advance team of the observers, Saif el-Yazal, responded: "We are here to see the facts on the ground. What we are seeing today is regretful. The important thing is for things to calm down."

Omar Idilbi, a member of the Syrian National Council, an umbrella opposition group, said the explosions were "very mysterious".

"They happened in heavily guarded areas that are difficult to be penetrated by a car," he said. "The presence of the Arab League advance team of observers pushed the regime to give this story in order to scare the committee from moving around Syria.

"The second message is an attempt to make the Arab League and international public opinion believe that Syria is being subjected to acts of terrorism by members of al-Qai'da."

One resident in the area of the attack said he was deeply sceptical of the official version of events.

Daoud, who declined to give his surname, said: "People had been told that there may be bombings. In that case how did these bombers get through?

"This is a very secure area and there had been further security with roads blocked off, which makes one think someone inside was responsible."

However, others felt the blasts were an attempt to introduce sectarian strife of the type seen in Iraq.

Haifa Nashar,45, blamed Qatar, the Sunni state that has become the leading supporter of the rebels in the Arab League. Wailing outside a damaged building, she shouted: "May God curse their souls!"