Sri Lankan troops battled to force the Tamil Tigers out of their last remaining strongholds in the north, while the rebels detonated a roadside bomb in the east that killed seven people, the military said Friday. The attack outside the eastern city of Trincomalee signaled that the rebels were turning to guerrilla tactics to attack the military. The government captured the east from the rebels in 2007, but attacks in the area have increased in recent months. On Friday, the rebels triggered a roadside bomb as a convoy escorted by the troops passed by, said military spokesman Brig. Udaya Nanayakkara. The bomb killed three air force troops and four civilians and injured six others, he said. Rebel officials could not be contacted for comment.