A bomb blamed on Tamil Tiger rebels tore through a cafe this evening in eastern Sri Lanka, killing 11 people and casting a cloud over crucial provincial elections scheduled for Saturday.

The elections were meant to be a final step in restoring normalcy to the eastern province, which the government freed from 13 years of Tamil Tiger rule last year.

To ensure a smooth poll, the government sent an unprecedented 28,000 police officers and an extra 4,000 soldiers to back up the thousands of troops already in the province, authorities said.

Despite the enormous police and military presence, the rebels blew up a small restaurant in Ampara, 220 kilometres east of Colombo, one of the largest towns in the eastern province, the military said.

Military spokesman Brigadier Udaya Nanayakkara said the blast, which killed 11 people and wounded 29 others, was clearly the work of the rebels, known formally as the Liberation Tigers of Tamil Eelam (LTTE).

"Yes definitely, it's the LTTE," he said.

"They have done similar explosion in Colombo and its suburbs. This was also done by the them."

Rebel spokesman Rasiah Ilanthirayan did not answer calls for comment, but the Tamil Tigers routinely deny responsibility for such attacks.

The group, blamed for more than 240 bombings and other attacks, is listed as a terror organisation by the United States and European Union.

A peaceful vote on Saturday would be a victory for the government and a morale boost in its continuing battle against the rebels.

But the blast showed the rebels - if they are responsible for the blast - still retain the ability to carry out attacks on civilians, even though the government has driven them out of the towns of the region.