A former general who became an opposition leader was among the dead in the explosion on Monday outside the newly opened offices of the United National Party in Anuradhapura.

"A suicide bomber went inside and exploded. My senior officer there said 22 people were killed and among the dead were Janaka Perera and his wife," KPP Pathirana, deputy inspector general of police, told the Reuters news agency.

Brigadier Udaya Nanayakkara, a military spokesman, blamed the Liberation Tigers of Tamil Eelam (LTTE), which has been fighting for an independent homeland for four decades, for the blast.

"The LTTE set off a suicide explosion. There are large number of casualties," he said.

"He [Perera] was a retired general who had fought the LTTE, and because of that they may have targeted him," Nanayakkara told Al Jazeera.

The United National Party was in government in February 2002 when a Norwegian-borkered peace process, which finally collpased earlier this year, was agreed.  

There was no immediate claim of responsibility, but the Tamil Tigers are known to have previously carried out suicide attacks. 

Military offensive

Sri Lanka's military has been involved in a major offensive against the LTTE, or Tamil Tigers, in the north of the island for more than a year in an attempt to finally defeat the group. 

"The military has been conducting quite an intensive offensive over the last few months and they are now apparently within a few kilometres of Kilinochchi, the de facto capital of the LTTE," Al Jazeera's Stephanie Scawen, reporting from the capital Colombo, said.

"How long it will take for them to overrun Kilinochchi will have to be seen, but obviously that would be the intention."

In a separate attack overnight, a roadside bomb killed two civilians and wounded another on a remote road in the Anuradhapura district, according to Sri Lanka's military.