The clash occurred in Ampara district 220 kilometers (130 miles) east of the capital, Colombo, said military spokesman Brig. Prasad Samarasinghe.

The rebel base was thought to be a ``threat to the main road'' where suspected rebels often activate roadside bombs targeting the military, Samarasinghe said.

He said 12 commandos were wounded in the fighting.

Meanwhile, the military said ground troops, backed by artillery, captured three Tamil Tiger bases and a smaller camp overnight in northeastern Trincomalee district, north of Ampara.

``We have forced the terrorists to flee from these three bases,'' Samarasinghe said, adding that another, smaller camp was also overrun. There were 100 to 150 rebels in the bases.

``They have suffered heavy casualties,'' Samarasinghe said, without providing a figure. But troops clearing the areas have found bloodstains on the jungle path, suggesting the rebels have suffered casualties, he said.

Trincomalee has a strategic port and serves as a base for the Sri Lankan navy and a major sea supply route to 40,000 Sri Lankan troops stationed in the Jaffna peninsula.

The rebels, formally known as Liberation Tigers of Tamil Eelam, tacitly acknowledged that Sri Lankan troops had taken over the Trincomalee bases. However, rebel officials were not available to comment on the clash in Ampara.

``We had hundreds of bases in that area. Many were closed years back, some were closed recently,'' Rasiah Ilanthirayan, the rebel spokesman, said from the insurgents' headquarters in Kilinochchi.

``It is a matter of walking into vacated places,'' Ilanthirayan said, suggesting that the bases were empty when Sri Lankan troops reached them.

``They are beating around the bush without reaching our core area,'' he said of the rebels' strongholds in the jungles and areas in the north, where the army has not begun operations.

The new military offensives coincided with reports that thousands of villagers were fleeing from rebel-held areas in the east, fearing new fighting between the guerrillas and government troops.

At least 13,685 Tamil refugees have crossed into government-held territory in Batticaloa district, Samarasinghe said.

The refugees fear their villages will become battlegrounds as fighting intensifies.

About 4,000 people have died in escalating violence in Sri Lanka since late 2005, when a Norwegian-brokered 2002 cease-fire faltered, European cease-fire monitors say. About 65,000 people were killed before the truce was signed.

The rebels have been fighting since 1983 to create a separate state in the north and northeast for the country's ethnic Tamil minority, following decades of discrimination by the Sinhalese majority.

Discuss this story Published: Fri Mar 9 08:07:40 EST 2007

``Measures that should be considered include: the use of evidence by video link, the physical protection of witnesses by a body independent of the police and army, and the temporary or permanent relocation of particularly vulnerable witnesses,'' said Birnbaum.

According to Sri Lankan law, a magistrate leads initial inquiries of a crime and based on available evidence determines grounds for further investigation and prosecution. Then witnesses are called.

``The Sri Lankan government needs to dispel serious concerns about whether the justice system is now able to carry out independent and credible investigations into who was responsible for these killings and to mount effective prosecutions,'' Birnbaum said.

Violence between government troops and Liberation Tigers of Tamil Eelam guerrillas escalated last August, after years of relative peace after a 2002 Norway-brokered cease-fire was signed.

Some 4,000 people have died in renewed violence limiting the truce agreement only to paper. More than 65,000 people died in the conflict before the cease-fire.

``This is an appalling atrocity,'' Birnbaum said. ``The killers could not have been in any doubt about who they were executing.''Discuss this story Published: Fri Mar 9 08:08:44 EST 2007