By Ranga Sirilal and Shihar Aneez
COLOMBO, Feb 9 (Reuters) - A female Tamil Tiger suicide bomber hiding among people fleeing Sri Lanka's war blew herself up on Monday, killing at least 28 civilians and soldiers and wounding 90, the military said.
The blast happened near Vishvamadu, a town in the north of the Indian Ocean island recently captured by soldiers battling to crush the Liberation Tigers of Tamil Eelam (LTTE) separatists and end a 25-year-old war.
The United States in a statement condemned it as "an apparent effort to discourage Tamils from leaving the conflict area". The military said it was the third suicide attack in a week.
Underscoring the challenge the military faces in separating combatants from civilians as the exodus of refugees picks up, officials said the bomber was in a group of people being checked for weapons by soldiers when she set off the bomb.
"Two officers and 18 others were killed from the army, two officers injured and 48 others injured. Eight civilians were killed and 40 others injured. Many of them are women and children," military spokesman Brigadier Udaya Nanayakkara said.
State TV footage taken after the blast showed a scene of bloodied bodies lying in a jungle clearing, among strewn suitcases and bags stuffed with personal belongings.
A soldier was shown carrying a child's motionless body and loading it into a truck next to a wounded adult.
Another image showed a man in a chair, his arm hanging lifelessly and a pool of blood at his feet.
The rate of civilians fleeing fighting between the military and the cornered LTTE has picked up sharply this week, with at least 17,300 escaping LTTE-held areas since Thursday -- out of at least 21,627 so far this year, according to military tallies.
Aid agencies say 250,000 people are trapped in a war zone measuring just 175 square km (67 sq miles), but the government puts the number trapped at about half that.
DESPERATE MEASURE
More than 50,000 soldiers are converging on a sliver of jungle in the Indian Ocean island's northeast to crush the LTTE -- now estimated to number no more than 2,000 hardcore fighters.
The government, aid agencies and rights groups have accused the LTTE of forcibly keeping civilians in the war zone as human shields and for use as conscripts and labourers.
The rebels deny that and accuse the government of intentionally targeting civilians, which the military denies.
The former head of intelligence for India's 1987-1990 peacekeeping mission in the Sri Lankan war, Col. R. Hariharan, said the civilian presence was the LTTE's last defence.
"It is a desperate measure. The refugees are getting out of control of the LTTE, so this flood will increase. This was a sort of a shock treatment," Hariharan, who spoke to Reuters by phone from Chennai, said of the blast.
The LTTE has a squadron of elite fighters known as the "Black Tigers" used for suicide missions, including one attack with an explosives-laden truck that killed 15 soldiers last week and another failed suicide blast, the military has said.
Analysts say that is the type of war the LTTE will fight once it is defeated as a conventional fighting force. The army's commander has said his troops are ready for that.
The Tigers have landed on U.S., E.U., Canadian and Indian terrorism lists, largely for their widespread use of the suicide blast as a weapon of war.
The LTTE is credited with inventing the suicide jacket, a bomb-laden vest, and of creating a culture of martyrdom. All fighters on duty wear cyanide capsules around their necks to be taken in case of capture, a symbol of their no-surrender mindset.
(Writing by Bryson Hull; Editing by Jerry Norton)