The Tamilnet web site said those killed on Sunday were supporters of renegade Liberation Tigers of Tamil Eelam
(LTTE) commander Vinayagamoorthy Muralitharan, known as
"Karuna", and included one of his deputies.
"The killings are confirmed, but we can't say who is dead
and who is responsible," a police official told Reuters.
Tamilnet said the assailants were believed to be gunmen
from the main faction of the LTTE. It said a Sri Lankan
military intelligence official was also among the dead.
The police official said the killings took place at a residence believed to be a Tamil rebel safe house in Kottawa, an outer suburb of Colombo.
Residents said the house - a plush double-storey building set in a rubber plantation and surrounded by a two metre (six feet) brick wall - had been rented about two weeks ago by a man believed to be an important key Karuna associate.
On Sunday police and army investigators swarmed over the
house looking for clues. In the driveway, police experts dusted
a Japanese saloon car for fingerprints as a bomb squad team checked the premises for booby traps.
Karuna, one of the most senior Tamil commanders, split from
the LTTE earlier this year, prompting a crisis in the group, which has been fighting for decades in a war that has claimed more than 64,000 lives.
The LTTE is run with an iron first by its senior commanders, and analysts say scores will be settled for months to come as a result of Karuna's split.
Although the LTTE has regained control of the eastern areas formerly commanded by Karuna, the group accuses the government of supporting him in order to drive a wedge through their ranks.
A team of Norwegian negotiators, led by deputy foreign minister Vida Helgesen, arrived in the Sri Lankan capital on Sunday afternoon in the latest attempt to re-start the stalled peace process.
The peace process faltered in April last year with government and Tigers divided over the agenda for resuming talks. The rebels want discussions based on their proposals for interim self-rule, while the government wants parallel talks on a final settlement.
Before leaving Oslo, Helgesen told Reuters that certain elements in the conflict "were playing with fire", and that the process was at a crucial stage.
"Sixteen months have passed without a high-level meeting
between the parties and that is a very long time," he said.
"We are not optimistic about getting them back to the
negotiating table because there is so little confidence between them."
Helgesen is due to travel to Kilinochchi in the rebel-held north on Monday to meet SP Thamilselvan, leader of the LTTE's
political wing, and to meet President Chandrika Kumaratunga and the prime minister in Colombo before he leaves on Thursday.