At least 15 people were killed and 25 wounded when suspected Liberation Tigers of Tamil Eelam rebels triggered a blast on a bus in eastern Sri Lanka on Monday.

The blast ripped through the crowded bus as passengers were getting off at a military check point just outside the town of Ampara, 350 km east of capital Colombo, police said.

"Three people were dead on admission while 12 more died after being taken for surgery," a hospital spokesman said, adding that about 25 people had been brought in with injuries.

The blast came as Sri Lankan President Mahinda Rajapakse was in New Delhi to attend the SAARC summit opening on Tuesday.

Police said that the Tiger guerrillas may have set off the blast as part of efforts to ease the pressure on their cadres facing military onslaughts in the region in recent weeks.

The latest blast came as the Tigers denied killing six civilians in the neighbouring Batticaloa district on Sunday night. The Tigers blamed the breakaway Karuna faction for the killings.