Story highlights Ahmed Omar Abu Ubaidah is the Islamic militant group's third leader

Al-Shabaab militants attack African Union forces, local government official says

Somalia ministry boosts security around government buildings

Intelligence reports indicate Al-Shabaab is planning attacks in Somalia

The Somalia-based militant group Al-Shabaab has named a successor to its leader killed in an American airstrike this week, a spokesman said Saturday.

The announcement came as Somalia braced for possible retaliation after Monday's killing of Ahmed Godane.

Al-Shabaab's new leader is Ahmed Omar Abu Ubaidah, spokesman Sheikh Ali Dheere said in an audio message posted online.

He is the group's third leader and was characterized as a low-ranking commander. No other information was available.

"The death of Godane will not stop the group from carrying out its terror operations," the spokesman said. "We lost our great leader Ahmed Godane and two other commanders in hands of the enemy on Monday night's U.S. airstrike."

His confirmation came after days of denying his death.

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Militants attack African Union troops

Somali Islamist militants ambushed African Union peacekeeping troops in southwestern Somalia, a local official said.

The militants attacked a convoy carrying Ethiopian AU troops in two locations between the towns of Qansahdheere and Burdhubo, said Hassan Mohamud Ali, district commissioner of the latter town.

The AU troops eventually stopped the attack and secured the area, Ali said. No information was available on the casualties.

The troops have a base in Burdhubo, which used to be held by Al-Shabaab before Somali and AU forces captured it in March. It's about 250 miles (400 kilometers) south of the capital of Mogadishu.

A Burdhubo resident said he could hear Saturday's clashes from the town.

"We are hearing heavy fighting and shelling," resident Ali Mohamed said.

Shortly before the attack, the nation's security ministry placed government buildings on high alert because of the killing of Godane.

Intelligence reports indicated the group is planning attacks in Somalia, according to Mohamed Yusuf, a spokesman for the security ministry.

'Symbolic and operational loss'

The U.S. military said it killed Godane in a thunderous attack Monday.

"Removing Godane from the battlefield is a major symbolic and operational loss to Al-Shabaab," said Rear Adm. John Kirby, a Pentagon press secretary.

Godane had been at the helm since the group started a campaign of terror in East Africa, killing Somali officials, aid workers and others in a spate of suicide bombings.

U.S. officials were tipped off to what Kirby called "actionable intelligence ... strong enough" to suggest his whereabouts.

Commandos flew in Monday and took the leader out with the help of drones and laser-guided missiles, Kirby said.

The man behind Al-Shabaab

Godane, who was also known as Mukhtar Abu Zubayr , became the leader of the militant group in 2008.

The group started off with a goal of waging a war against the Somali government in an effort to implement a stricter form of Islamic law, or sharia.

But it has shifted focus to terrorist attacks beyond Somalia. It has targeted East African states supporting the Somali government, especially Uganda and Kenya.

A year ago, militants raided a mall in the Kenyan capital of Nairobi in an audacious siege that lasted days and left 67 people dead.

The attack wasn't the group's first strike outside Somalia.

In 2010, it carried out suicide bombings in the Ugandan capital, Kampala, killing more than 70 people.

Under Godane, the terror group became a formal ally of al Qaeda.