Al-Qaeda has backed the new Islamist chief of Somalia's Shebab insurgents after his predecessor was killed in a US air strike last week, according to a statement broadcast Monday on Shebab radio.

"Our prayers also go to the new Emir, Ahmad Umar Abu Ubaidah to gain strength to continue the jihad of brother Abu Zubayr," the unsigned statement said from the Yemen-based branch of the extremist franchise, Al-Qaeda in the Arabian Peninsula.

The statement, which could not be independently verified, was broadcast repeatedly on the Shebab's official Radio Andalus.

Ahmed Abdi Godane, also often known as Abu Zubayr, was killed by a US air strike last week. He was a ruthless kingpin of Al-Qaeda's main African affiliate.

It offered its "condolences" for Godane's death.

"He met Allah as he wished, and we pray that he is accommodated well for his relentless jihad," the statement read.

"Prayers are with him, that his martyrdom be accepted by Allah for his defence of Islam and Muslims."

The Shebab, who named Abu Ubaidah as leader in a statement on Saturday, also renewed a pledge of allegiance to Al-Qaeda chief Ayman al-Zawahiri, Osama bin Laden's successor.

The statement vowed revenge for the killing of Godane.

"You will feel the pain soon and there will be an accountability in days coming, each one has his own days," it added.

Very little is known about Abu Ubaidah, a hardliner who had reportedly been close to Godane, and who had overseen the group's transformation from local insurgency to major regional guerrilla threat.