A suicide bomber killed least 27 people, including an opposition politician and former military officer who spearheaded military operations against Tamil rebels, and injured 94 others in north-central Sri Lanka Monday, police said.

Retired Major General Janaka Perera was taking part in the opening of a political office of his party - the main opposition United National Party (UNP) - in Anuradhapura, 180 kilometres north of Colombo, when the bomber exploded.

Perera, the opposition leader of the provincial council in the North Central province, commanded the army in the Tiger stronghold of Jaffna peninsula in the mid-1990s.

Perera's wife, as well as a chief organizer for the district, Dr A Johnpulle and his wife, were among those killed.

Military spokesman Brigadier Udaya Nanayakkara said the attack was carried out by a Tamil rebel suicide bomber.

UNP officials earlier said the attacker had posed as a lawyer to get close to Perera when he detonated himself, but other witnesses said the bomber was dressed in a T-shirt and rushed towards the politician at the end of the ceremony.

After retiring from the military, Perera served as Sri Lanka's ambassador to Australia and Indonesia before returning home and joining the UNP.

In 1999 Tamil rebels assassinated Major General Lucky Algama, a supporter and military advisor of the UNP, in a similar attack.

The opposition accused the government of failing to provide security for the event.

"We have to blame the government as they failed to provide adequate security to the major general, despite knowing that he was a target of the Tamil rebels," party general secretary Tissa Attanayaka said.

Perera had to seek the intervention of the Supreme Court to obtain security during the campaign for elections held in August, but the protection was retired after the voting.

The fresh attack came as government troops stepped up their military campaign against Tamil rebels in the north and were closing in on a town held by rebels.

The troops were said to be 2 kilometres south of Kilinochchi town, 380 kilometres north of Colombo. The town was used as the main administrative base of the rebels of the Liberation Tigers of Tamil Eelam (LTTE).

The government had warned that rebels may carry out attacks to distract the security forces.