Ban Ki-Moon, the UN secretary general, sided with the Syrian regime on Friday by blaming al-Qaeda for a double bombing that killed 55 people in Damascus last week.

Mr Ban’s assessment is likely to be seized on in Damascus, where President Bashar al-Assad has long claimed that the rebellion against his rule is dominated by extremists bent on turning Syria into an Islamist state.

“Very alarmingly and surprisingly, a few days ago there was a huge, serious, massive terrorist attack,” the secretary general said. “I believe that there must be al-Qaeda behind it. This has created again very serious problems.”

Both Damascus and Aleppo, Syria’s second city, have witnessed a spate of mass-casualty bombings, generally targeting civilians, since last December as the country’s uprising entered its tenth month.

On each occasion, Mr Assad has been quick to blame al Qaeda and a shadowy group claiming affiliation to the network has claimed responsibility for a number of the attacks, including last week’s bombing.

Mr Ban did not provide evidence for his claim, nor did he indicate whether he believed that al-Qaeda was responsible for the earlier bombings.

Opposition officials, as well as a number of officers who have defected from the army, claim that the regime itself is behind the attacks as part of a conspiracy to discredit the uprising and rally Syrians behind the president.

But a growing number of Western diplomats and analysts have suggested that Islamist extremists inspired by al Qaeda are operating on the fringes of the uprising, even if their message of violence is neither blessed nor wanted by the vast majority of the opposition.

Beyond sowing chaos, it is unclear what the motivation of such extremists is. Many are believed to have crossed the border from Iraq, where they were involved in the insurgency against US forces in the years following the invasion that toppled Saddam Hussein.

Although al Qaeda has long dreamed of overthrowing many of the Middle East’s leaders, its followers have played little part in the uprisings have swept the region. Following the American military withdrawal from Iraq last December, some may have concluded that Syria represented a more fertile territory for their ambitions, Western diplomats suggested.

“Al Qaeda has been left behind by the Arab Spring,” one said. “They see in Syria an opportunity to re-establish their foothold.”

Mr Ban said he believed that “more than 9,000, at least, maybe 10,000 people” have been killed over the course of the 15-month uprising. “It has reached an intolerable situation now,” he told a youth event at UN headquarters.

Struggling to compile accurate statistics because of Syria’s chaos, the UN has stopped estimating a death toll. But it said in March that more that 9,000 civilians had died, while Susan Rice, the US ambassador to the UN, said last month that the figure had passed 10,000. Syria’s opposition says 11,000 have been killed.

The violence continued on Friday, with security forces opening fire on demonstrators in Douma, near Damascus, and in Aleppo, which saw its largest protests since the uprising began. The opposition have struggled to win open support in Aleppo, which is considered crucial to their chances of success.

Mr Assad’s army also shelled the cities of Rastan and Homs. Although such artillery attacks have dwindled since the deployment of UN observers last month, they are far from infrequent and have led to calls on the international community to admit that the peace plan brokered by Kofi Annan, the UN and Arab league envoy, has failed.

The Norwegian head of the 200-strong observer mission, Maj ten Robert Mood, warned that it would be impossible for it to achieve a permanent end to the violence unless both sides in the conflict agreed to hold genuine talks.

Negotiations are an integral part of Mr Annan’s plan but the prospect for dialogue looks remote. (© Copyright of Telegraph Media Group Limited 2012. 05/19/12)