The Somali Islamist militant group al Shabaab confirmed today that its leader Ahmed Godane had been killed in a US air strike this week and named a new leader, promising "great distress" to its enemies.

US forces struck Godane's encampment in south-central Somalia with Hellfire missiles and laser-guided munitions on Monday, but the Pentagon did not confirm his death until Friday.

In a statement, al Shabaab, affiliated to al Qaeda, named its new leader as Sheikh Ahmad Umar Abu Ubaidah, and warned its enemies to "expect only that which will cause you great distress".

Al Shabaab also said two of Godane's companions had been killed in the attack.

The Pentagon said on Friday that Godane's killing was a "major symbolic and operational loss" for al Shabaab.

Since taking charge of al Shabaab in 2008, Godane had dramatically raised the group's profile, carrying out bombings and suicide attacks in Somalia and elsewhere in the region, including last September's attack on the Westgate shopping mall in Nairobi, Kenya, in which 67 people died.

Godane publicly claimed responsibility for the Westgate attack, saying it was revenge for Kenyan and Western involvement in Somalia and noting its proximity to the anniversary of the Sept. 11, 2001, attacks on the United States.

Shabaab said Godane had left behind a group of men who would continue their holy war.

"Avenging the death of our scholars and leaders is a binding obligation on our shoulders that we will never relinquish or forget, no matter how long it takes," the statement said.

Somalia's government, with support from African peacekeepers and Western intelligence, has battled to curb al Shabaab's influence and drive the group from areas it has continued to control despite being expelled from Mogadishu in 2011.