Mogadishu - A senior al-Shabaab commander and about 20 of his followers have pledged allegiance to Islamic State (ISIS), the first move of its kind to emerge in the Somali militant group.
There was no immediate reaction from al-Shabaab's overall leadership, which aligned itself in 2012 to al Qaeda, a group that has declared Islamic State's leader illegitimate.
Experts have been watching to see if the rise of Islamic State in Syria, Iraq and other battlefields, would draw al-Shabaab's public support, but said the impact of any such alliance would be largely symbolic given geographical distance would hinder an exchange of material supplies.
"We, the mujahideen of Somalia, declare allegiance to the caliph as Ibrahim ibn Awad ibn Ibrahim al-Awad al-Qurashi," Abdiqadir Mumin, an al-Shabaab commander in the Puntland region of Somalia, said in an audio tape published on YouTube.
Nigerian militants Boko Haram also pledged allegiance to Islamic State this year, a move seen as highlighting a desire by African jihadists to link up with others in the Middle East and elsewhere.
ISIS has accepted pledges of allegiance from groups in the Middle East, Afghanistan, Pakistan and North Africa.
A follower of al-Shabaab's Mumin confirmed the veracity of the recording declaring allegiance to al-Qurashi, better known as Abu Bakr al-Baghdadi, the leader of Islamic State and self-proclaimed caliph of the Muslim world.
"Senior leader Abdiqadir Mumin and his 20 fighters, including me, joined ISIS," one of Mumin's supporters told Reuters by telephone, using one acronym for Islamic State.
Mumin had been based in the Galgala hills in Somalia's semi-autonomous Puntland region, said the supporter, who asked not to be identified. The 20 came from a group of 300 in Galgala, he said, adding that his group had now moved to another area.
"The other fighters rejected us and remained in the Galgala hills," he said.
There are no clear figures for the strength of al-Shabaab, but diplomats put it at several thousand fighters. One expert said the announcement suggested a small split in the ranks.
Al-Shabaab, which ruled much of Somalia for several years until 2011, was driven out of most urban centres by an offensive launched by African Union forces and Somali troops last year. Some were driven north to Puntland, experts say.
Puntland's security minister dismissed Mumin's declaration. "Puntland forces are ready and determined to eliminate ISIS," Abdi Hirsi Ali said.