Around 150 members of terror group Al-Shabaab have been killed in a U.S. airstrike in Somalia as they were preparing to launch an attack, Pentagon chiefs confirmed.

American drones and manned aircraft dropped bombs and launched Hellfire missiles on the Raso Camp, an Al-Shabaab training facility 120 miles north of the Somalian capital Mogadishu.

Defense officials said the group had been planning a 'large-scale attack' for some time but appeared to be nearing the final stages of preparation, and so ordered the strike.

It is not yet known whether any senior figures within the terror group were among those killed in the strike, which took place overnight on Sunday.

Around 150 members of terrorist group Al-Shabaab have been killed after American drones and manned aircraft launched Hellfire missiles and dropped bombs on a training camp in Somalia (file image)

Pentagon officials said they had been watching an Al-Shabaab training camp around 120 miles north of the capital Mogadishu for several weeks before deciding to launch the strike

Officials estimated that as many as 200 fighters had been at the camp, including a number of trainers. There were no known civilian casualties. Al-Shabaab is believed to have between 7,000 and 9,000 fighters in total.

Mohamed Ali Gele, one of the group's most senior leaders, was not among those killed after being captured in the country's south just hours earlier.

African union troops operating in war-torn Somalia announced they had captured Gele earlier today in the tiny village of Qoryoley.

Commander Ahmed Gabow Bule said: 'The joint forces captured Mohamed Ali Gele, Shabaab’s Commander for Qoyoley, Janale towns and many other villages in the region.

'We were looking for him for a period of time. We arrested him in a security operation which was conducted in the region.

'The police are questioning him; we will transfer him to the central government of Somalia after the investigation. This was a very successful operation that resulted in the arrest of one of the senior Al-Shabaab commanders.'

Formed in 2006, Al-Shabaab - which means 'the youth' in Arabic - regularly carries out attacks in the east of Africa, including in Somalia which is widely regarded as the world's most failed state.

The group's stated aim is to oust the Somali government in order to create a territory which can be ruled according to their strict interpretation of Sharia law. They are affiliated with Al Qaeda.

The first attack credited to the group was a car bombing in March 2007 against Ethiopian troops in the Somalian capital of Mogadishu which killed 73 people.

In their latest notable attack, Al-Shabaab attempted to kill a number of 'senior Western officials' on board a flight from Mogadishu to Djibouti with a laptop bomb.

Defense officials said the group had been planning a 'large-scale attack' for some time but appeared to be moving into the final stages of preparation, prompting the attack (file image)

Al-Shabaab was behind the recent bombing of a Daallo Airlines plane en route from Mogadishu to Djibouti, blowing a hole in the side of the aircraft (pictured)

The sophisticated device managed to make it through airport security before detonating on board the plane, officials said.

However, rather than destroying the aircraft as planned, the bomb instead blew a small hole in the side of the aircraft which caused the body of the dead attacker to get sucked out.

The main suspect is believed to be a Somali national known as Abdullahi Abdisalam Borleh. The bomber had been carefully instructed where to sit and how to trigger the deadly device.

Following the attack the plane was forced to come back into land at Mogadishu airport.

Earlier today a roadside bomb, believed to have been planted by the group, wounded two Somali soldiers and an African Union peacekeeper near the airport in Beledweyne.

The bomb was hidden in a 'paper bag', according to local security officials, who said it is not yet clear if the device was meant to end up on a plane.

Meanwhile the Australian Navy said it seized a huge shipment of weapons, including 2,000 AK-47 rifles, 100 rocket-propelled grenade launchers, and 49 PKM machine guns that was bound for Somalia.

The haul was discovered hidden under nets on a fishing boat that was stopped off the coast of Oman, navy officials said.