Nairobi — The Somali militant group al-Shabab has formally joined al-Qaida, according to a video translation released Thursday of a message from al-Qaida's leader.

Ayman al-Zawahri gave "glad tidings" that al-Shabab had joined al-Qaida, according to the translation of the 15-minute video by the Site Intelligence group.

"Today, I have glad tidings for the Muslim Ummah 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 Zio-Crusader campaign and their assistants amongst the treacherous agent rulers," he said.

Al-Shabab leaders have pledged allegiance to al-Qaida in the past, releasing a video in 2009 called "At Your Service Osama!" The same year, former al-Qaida leader Osama bin Laden released a video in which he made encouraging comments about the Somali insurgency.

But the new al-Zawahri video which was posted on an Islamic Internet forum on Thursday is the first formal welcoming of al-Shabab by the new al-Qaida leader. The new video also featured al-Shabab chairman Mukhtar Abu Zubeyr, also known as Godane, pledging allegiance to al-Zawahri.

Somalia's al-Shabab militia is a mix of conscripts, paid fighters, clan militias, and ideologues. It counts a few hundred foreign fighters among its ranks. Most are drawn from other East African nations but a few have traveled from as far afield as Pakistan and Chechnya.