Somali militant group al-Shabab has executed three of its own members for alleged spying on behalf of U.S. and British intelligence agencies.

A pro-al-Shabab website says the three men were executed Sunday in the town of Merka.

An al-Shabab judge said one man had admitted to working for British spy agency MI6 and handing over Muslims to authorities in the breakaway state of Somaliland.

He said the other two planted devices in cars that allowed U.S. drones to locate and attack foreigners working with al-Shabab.

The two foreigners were killed earlier this year in drone strikes in towns near Mogadishu.

Hundreds of foreigners are believed to be in Somalia assisting al-Shabab, which announced a formal alliance with the al-Qaida terrorist network in February.

Al-Shabab is trying to overthrow Somalia's transitional national government and turn the country into a strict Islamic state.

The group once controlled much of southern and central Somalia, but has lost most of its territory to African Union, Somali government, and Kenyan and Ethiopian forces.