Somalia's Islamist group al-Shabab has named Ahmad Umar as successor to former leader Ahmed Abdi Godane, who was killed in a US air strike.

The group announced the move in an online statement, vowing to take revenge for Godane's death.

Somalia's authorities earlier put the country on alert for possible retaliatory attacks by al-Shabab.

The alert came as the US confirmed the death of Godane in air strikes south of Mogadishu on Monday night.

'Bitter consequences'

Little is known about Ahmad Umar, who is also known as Abu Ubaidah.

Abu Mohammed, one of al-Shabab's commanders, said the decision to appoint him was unanimous.

In a statement, al-Shabab also warned: "Avenging the death of our scholars and leaders is a binding obligation on our shoulders that we will never relinquish nor forget no matter how long it takes."

"By the permission of Allah, you will surely taste the bitter consequences of your actions."

The announcement of the new leader came just minutes after al-Shabab themselves confirmed the death of Godane.

Earlier on Saturday, Somali National Security Minister Kalif Ahmed Ereg told reporters: "Security agencies have obtained information indicating that al-Shabab is now planning to carry out desperate attacks against medical facilities, education centres and other government facilities."

Mr Ereg "congratulated the Somali people" on Godane's death, adding: "The security forces are ready to counter their attacks and we call on people to help the security forces in standing against violent acts."

Ahmed Abdi Godane:

• US put $7m (£4m) bounty on his head in 2012
• Pledged allegiance to al-Qaeda in 2009
• Became al-Shabab's top commander after US air strike killed his predecessor Aden Hashi Ayro in 2008
• Sentenced to death in absentia for 2008 attack in Somaliland's capital, Hargeisa
• Studied in Sudan and Pakistan, where he became radicalised
• Said to have fought in Afghanistan
• Was reputed to be a good orator and poet
• Also known as Mukhtar Abu Zubair

Ahmed Abdi Godane profile

Somalia's President Hassan Sheikh Mohamud issued a statement on Friday urging militants to embrace peace after the death of their leader.

He announced a 45-day amnesty for militants who were willing to renounce the group.

Godane was one of the US state department's most wanted men.

It had placed a bounty of $7m (£4.2m) on his head.

The US has supported the African Union (AU) force that has driven al-Shabab out of the capital Mogadishu and other towns since 2011.

The al-Qaeda-linked fighters want to overthrow the UN-backed Somali government and frequently attack government targets as well as neighbouring countries that provide troops to the AU force.

The al-Shabab leader had publicly claimed the group's responsibility for the deadly Westgate shopping centre attack in Kenya in September last year.