The Sahara-based al-Mourabitoun Islamist group has pledged allegiance to the Islamic State, the Mauritanian news website Alakhbar said, citing a recording it had received from a spokesman for al-Mourabitoun.

It was not immediately possible to verify the recording, but Alakhbar regularly receives messages from Islamist groups operating in the region.

Nigeria's Boko Haram has already pledged allegiance to Islamic State, but al-Mourabitoun would be the first Sahara-based outfit to link up with the Sunni Islamist group.

In the recording, posted on the Alakhbar website, a speaker calling himself Adnan Abu Waleed al-Sahrawi says al-Mourabitoun pledged allegiance to Islamic State's self-proclaimed caliph Abu Bakr al-Baghdadi and urged other jihadi groups to do likewise.

Islamic State, an ultra-hardline offshoot of al Qaeda, has declared a caliphate in captured territory in Iraq and Syria and has gained global notoriety for posting videos of its members killing Arab and Western hostages.

Al-Mourabitoun was formed in 2013 by the unification of fighters loyal to veteran Algerian jihadist Mokhtar Belmokhtar, a former al Qaeda fighter, and MUJWA, another Islamist group operating in West Africa that was headed by Sharawi.

The group claimed responsibility in March for a rare attack in Mali's capital that killed five people, including two foreigners.

Islamists that jointly occupied northern Mali in 2012 have been scattered from the main towns they once controlled by a 2013 French offensive, but they continue to attack local and international forces in Mali.