The US has said its military forces have carried out an operation against al-Qaeda-linked al-Shabab fighters in Somalia.

"We are assessing the results of the operation and will provide additional information as and when appropriate," said spokesman John Kirby on Monday.

A senior Somali intelligence official said a US drone targeted al-Shabab leader Ahmed Abdi Godane as he left a meeting of the group's top leaders, according to the AP news agency.

Godane, also known as Mukhtar Abu Zubeyr, is the group's spiritual leader under whose direction the Somali fighters forged an alliance with al-Qaeda.

The Somali official, speaking to the AP on condition of anonymity, said intelligence indicated Godane "might have been killed along with other militants".

The official said the attack took place in a forest near Sablale district, 170 kilometers south of the capital, Mogadishu, where al-Shabab trains its fighters.

Army advancements

The US military assistance comes as Somalia's army and African Union (AU) troops are continuing a major offensive against the armed fighters.

In the north of the country, security forces say they have captured districts in the Hiran region, without a single shot being fired, according to Al Jazeera's Mohammed Adow, reporting from Fidow, on the border of middle Shabelle and Hiran regions.

Government forces are also seeking to capture the seaside port of Barawe - al-Shabab's official headquarters - south of Mogadishu.

On Monday al-Shabab fighters carried out a car bomb and gun attack against an intelligence headquarters in central Mogadishu, leaving at least seven fighters and five others dead.

Al-Shabab fighters have targeted key areas of the Somali government or the security forces in an apparent bid to discredit claims by the authorities - who are backed by the African Union's 22,000-strong AMISOM force - that they are winning the war against the armed group.

The armed group is fighting to topple Somalia's internationally-backed government, and regularly launch attacks against state targets, as well as in neighbouring countries that contribute to the AU force.