The Tamil suicide bomber who targeted Sri Lanka's top general used her pregnancy to meticulously plan the attack, an investigator said. Officials previously said the bomber had only pretended to be pregnant, but the investigator said hospital records showed she actually was.

Her attack Tuesday killed 11 people and wounded army commander Lt. Gen. Sarath Fonseka and 25 others. It unleashed fighting between government troops and Tamil Tiger rebels that has posed the most serious threat yet to a four-year cease fire.

The military launched two days of air strikes against the rebels on Tuesday and Wednesday in apparent retaliation for the suicide bombing. The rebels say the strikes killed 12 and sent thousands fleeing their homes.

The bomber identified as 21-year-old Anoja Kugenthirasah used her pregnancy to conceal explosives and get inside a maternity clinic in the army's heavily fortified headquarters where she attacked the commander, said the investigator, who spoke on condition of anonymity because he was not authorized to speak to the media.

The woman is believed to have been a member of the dreaded Black Tigers suicide squad.

Fonseka, a battle-hardened soldier with 35 years in the infantry, was appointed to the military's top post after President Mahinda Rajapakse took office in November. He became a formidable enemy of the Tamil Tigers.

The investigator said Kugenthirasah had fake identification showing she was the wife of a clerk working for the Sri Lankan army and indicating she was pregnant.

Every Tuesday, the military hospital inside army headquarters in the capital Colombo holds a maternity clinic, and Kugenthirasah had visited three times, getting to know the guards and learning Fonseka's routine, the investigator said. The general went home for lunch around 1:30 p.m.

On Tuesday, Kugenthirasah arrived a half-hour ahead of the clinic opening and stood in front of the hospital, which is beside the road that Fonseka took when he left the headquarters.

As the general's car approached, she moved closer. One of Fonseka's motorcycle escorts shouted at her to get away, but she detonated the bomb shortly afterward. Five of Fonseka's escorts were among those killed in the blast.

Media Minister Anura Priyadarshana Yapa said he was aware of the initial findings of the bombing investigation but declined to comment until it was over.

The Black Tigers are renowned for their skill at suicide bombings against military, government and civilian targets. Victims have included former Sri Lankan President Ranasinghe Premadasa and former Indian Prime Minister Rajiv Gandhi.

The Tiger rebels have fought the government since 1983 to create a separate state for ethnic minority Tamils, accusing the majority Sinhalese-dominated state of discrimination.

On Dec. 4, the Tigers carried out the first major attack since the 2002 cease-fire, killing 12 navy sailors. Dozens of rebel attacks followed.

Sri Lanka's military at first exercised restraint, but Fonseka urged retaliation and the military began to return fire when attacked.

In a sign that tensions may be easing, however, the military said Thursday it would halt airstrikes if the insurgents stopped their attacks. On Friday, the government reopened roads linking rebel-held territory with government-controlled areas.

CountryWatch: Sri Lanka

The U.N. High Commissioner for Refugees said between 7,000 and 8,000 people were displaced in the recent air force bombing of rebel bases. The agency asked for immediate access to affected villages.

"The loss of life, the new displacement of families, the destruction to businesses and property, as well as threats to humanitarian workers, are creating a climate of fear and tension for civilians," Jan Egeland, the U.N.'s Emergency Relief Coordinator, said in a statement, calling on both sides to "to ensure full protection of civilians."