A suspected rebel suicide bomber killed 20 soldiers and eight civilians when she blew herself up Monday at a facility where government forces were processing Sri Lankans fleeing the northern war zone, the military said. The bombing was the first major suicide attack in Sri Lanka in more than a month and led to fears the Tamil Tiger separatists _ boxed in by the military and on the verge of defeat _ will increasingly turn to guerrilla warfare in their battle against government forces. Following a string of victories, the military backed the rebels into a small strip of land on the northeastern coast, where the Red Cross estimates 250,000 civilians are also trapped, according to a report of Associated Press. On Monday morning, more than 800 civilians had crossed the front lines and were being searched by soldiers before being sent to camps farther south, military spokesman Brig. Udaya Nanayakkara said. When the attacker was frisked, she set off the bomb she was wearing, killing 28 people, he said. The blast also wounded 24 troops and 40 civilians, he said.