Pakistan's army says a suicide attack on a military unit has killed three soldiers and wounded seven in Swat Valley, in the Kabal area.

A military statement says the suicide bomber detonated his explosives' vest near an empty lot used by the soldiers for sports and exercise on Saturday.

Security forces have cordoned off the area and are searching for possible accomplices of the bomber.

No group immediately claimed responsibility for the attack.

Islamic militants ruled the picturesque Swat Valley from 2007 until a massive military operation routed them from the area in 2009. The operation involved evacuating 2 million people from the valley. They were able later to return to their homes.

Saturday's attack was the first in over three years in the valley.