Dubai - Al-Qaeda announced on Thursday that the Somali militant group al-Shabaab was joining its ranks in an apparent bid to boost morale and sharpen a threat to Western targets diminished by months of setbacks including the loss of founder Osama bin Laden.

One analyst said the connection could signal that the insurgents, known as resourceful, determined and increasingly Web-savvy, had al-Qaeda's approval for attacks against the West.

In a video posted on Islamist forums on Thursday, al-Qaeda leader Ayman al-Zawahri said: “Today, I have glad tidings for the Muslim ummah (nation) that will please the believers and disturb the disbelievers, which is the joining of the Shabaab al-Mujahideen Movement in Somalia to Qaedat al-Jihad to support the jihadi unity against the Zionist-Crusader campaign and their assistants amongst the treacherous agent rulers.”

“I appeal to our people in Somalia not to follow those who teach ill, and the weak leaders who brought the crusader rabble to the land of pure Islam.”

The clip included an audio recording by al-Shabaab's leader Sheikh Abu Zubeyr, in which he pledged allegiance to Zawahiri, who took over the reins of al-Qaeda last year following the killing of bin Laden in a US attack in Pakistan.

Al-Shabaab, which controls large areas of Somalia, voiced support for Zawahri soon after he took over al-Qaeda and has had openly declared links to the network for more than two years.

While counter-terrorism experts say al-Shabaab has received advice and training from some members of al-Qaeda, it has tended to see itself more as an ally or affiliate than a direct outpost of the core organisation.

Initial Western official reaction was dismissive, pointing to the apparent weakness of al-Qaeda's top leadership, based in the mountainous border area between Afghanistan and Pakistan.

“Zawahiri's announcement just formalises what everyone already knew: al-Shabaab is an affiliate of al-Qaeda. This doesn't change the fact that al-Qaeda's core is still suffering and trying to remain relevant,” a US official said on condition of anonymity.

Analysts said the move appeared partly a propaganda gambit by an al-Qaeda leadership weakened by drone strikes and a failure to carry out a major successful attack in the West since 2005. But there might be more menacing consequences, some said.

“Al-Qaeda needs to project power and influence, particularly given its own operational impotence. A merger with al-Shabaab gives it the means to do so and it is a low risk, resource cheap solution for al-Qaeda's central leadership,” Australian al-Qaeda scholar Leah Farrall told Reuters.

“It stamps Zawhiri's authority on al-Qaeda and allows him to reinforce al-Qaeda's pre-eminence at a time when it has been waning. Al-Shabaab's acceptance under the al-Qaeda umbrella probably came with permission from Zawahiri for the group to launch external operations against the West,” she added.

Will Hartley of IHS Jane's said: “It seems unlikely that this will translate into any kind of practical operational co-ordination in the foreseeable future. But should this announcement be confirmed the Shabaab may be expected to carry out a signature 'Al-Qaeda type' attack, possibly in Kenya.” - Reuters