Spokesman Captain Jeff Davis said the strike hit a training camp where a “large-scale” attack was being planned.

“We know they were going to be departing the camp and they posed an imminent threat to US and [African Union] forces,” Captain Davis said.

“Initial assessments are that more than 150 terrorist fighters were eliminated,” he added.

Mr Davis said the strike, by both drones and manned aircraft, took place on Saturday and targeted Raso Camp, a training facility about 120 miles (195km) north of the capital, Mogadishu.

The camp had been under surveillance for some time, according to Mr Davis. “There was a sense that the operational phase was about to happen,” he said.

He said the group had neared the completion of specialist training to conduct “offensive operations”, but did not give any details about the alleged plans.

Al-Shabab, an affiliate of al-Qaeda, was pushed out of Mogadishu by African Union peacekeeping forces in 2011 but has continued to launch frequent attacks in its bid to overthrow the Western-backed government.

The group has said it carried out a string of recent attacks including a twin bombing at a busy restaurant in the Somali city of Baidoa last month.

Also on Monday, the Australian navy said it had seized a huge cache of weapons on a fishing boat off the coast of Oman that was apparently heading for Somalia.

Grenade launchers, machine guns, and 2,000 assault rifles were concealed under fishing nets, a Navy spokesman said.

Source: BBC