The country's third-highest ranking military officer was killed, along with three others, on Monday when the bomber blew himself up next to the general's car, officials said. Five others were wounded.
The authorities blamed the country's separatist Tamil Tiger rebels for the attack. Keheliya Rambukwella, the chief government spokesman, said it was a serious blow to the cease-fire.
The blast "carries the hallmark of the LTTE," Rambukwella said, using the initials of the insurgents' formal name, the Liberation Tigers of Tamil Eelam, who have long used suicide bombers in major attacks.
There was no comment from the rebels, but a pro-rebel website reported the attack without comment.
Civil war fears
Four months of violence have brought Sri Lanka dangerously close to the brink civil war, and Monday's blast - a rare attack so close to the capital - came just over two months after the Tigers tried to kill Sri Lanka's military commander in a similar bombing in Colombo.
Lieutenant-General Sarath Fonseka escaped the attack with injuries, but at least 12 others died in that blast.
Monday's attack on Lieutenant-General Parami Kulatunga took place close to Kulatunga's home in Pannipitiya, 15km (nine miles) southeast of Colombo's city centre.
The violence has raised fears of
another round of civil war
Kulatunga was a combat veteran who had led numerous operations against the rebels in Sri Lanka's northeast, the main theatre of fighting during a two-decade long near full-scale war.
Military spokesman Brigadier Prasad Samarasinghe said Kulatunga survived the initial blast, but died on the way to the city's National hospital.
An hour after the explosion, the general's Peugeot was still on fire. Another vehicle in the general's convoy, a pickup-truck, was also damaged.
The blast also killed the general's driver, a security guard and a civilian passerby, the military said. Five other bystanders were wounded and admitted to a hospital.
Perceived discrimination against Sri Lanka's 3.2 million Tamils, most of whom are Hindu, led the Tigers to take up arms in 1983. The resulting war on this tropical island of 19 million people - nearly three-quarters of them Buddhist Sinhalese - left more than 65,000 people dead before a 2002 cease-fire.
Sri Lankan Tamils say they are
discriminated against by Colombo
But talks to build on the truce soon faltered, and in the past year sporadic shootings and bombings have escalated into near-daily violence. Almost 700 people, more than half of them civilians, have been killed since April.
The rebels' separatist war is mostly confined to the northeast, where they want to carve out a separate Tamil homeland, though they do sometimes target people in Colombo.
In July 2004, a rebel suicide bomber targeted Douglas Devananda, a government minister and a moderate Tamil leader who opposes the rebels. The bomber detonated explosives, killing four people, while being frisked at a police station.