"Our Central Command is discussing about possible defensive measures we need to take to protect our Tamil people," senior rebel leader Seevaratnam Puleedevan told The Associated Press from the rebel town of Kilinochchi.

He said the air raids have left "a lot of casualties," but gave no figures.

A doctor at the hospital where the bus victims were taken, S.B. Bothota, said 15 schoolchildren were among the 64 killed. Another 78 people were wounded, he said.

At the hospital morgue, bodies of the victims were laid in rows. Some victims were relatives of a policeman killed Monday, apparently by rebels. They were heading to the slain man's funeral when the explosion tore through their bus.

Samarasinghe blamed the Tigers for the explosion, saying their "motive is to create terror." Police said the victims were primarily ethnic Sinhalese.

But Puleedevan countered the government's accusation by suggesting the attack could be "the work of forces seeking to create ethnic tension between the Sinhalese and the Tamil population."

"The Liberation Tigers condemn the attack on civilians in strongest possible terms," Puleedevan was quoted as saying by TamilNet.

The Liberation Tigers of Tamil Eelam fought for 20 years to carve out a separate homeland in Sri Lanka's north and east for the country's 3.2 million minority Tamils, who are largely Hindu. The majority of Sri Lankans are Sinhalese Buddhists.

A cease-fire four years ago ended large-scale fighting, but violence has persisted, intensifying following the assassination last August of Foreign Minister Lakshman Kadirgamar. The government blamed the killing on the Tigers.

Four months later, the Tigers killed 12 navy sailors -- the first major attack in four years -- and the situation on the ground has only deteriorated since then, with violence that has left more than 600 soldiers, rebels and civilians dead.

Both sides have blamed the other for the renewed violence, and the Tigers also routinely blame a breakaway rebel faction for attacks on civilians. Diplomatic efforts to quell the violence and get the peace process back on track have not progressed very far.

The Tigers pulled out of peace talks in April, and then last week scuttled negotiations by refusing to meet representatives of the government side after arriving in Oslo, Norway, the venue for the talks.