The victim in Colombo was a suspected Tamil Tiger rebel who was seriously wounded when police found him while patrolling near a newspaper office of a pro-government Tamil group opposed to the rebels, said Brig. Daya Ratnayake, a military spokesman.
Police rushed the victim to a nearby hospital but he subsequently died, Ratnayake said.
The office belongs to the pro-government Eelam People's Democratic Party, which bitterly opposes the Tamil Tiger rebels, who accuse the party of backing a renegade faction that broke away from the mainstream rebel movement a year ago.
The split sparked internecine clashes that have killed scores, mainly in Sri Lanka's volatile east.
In recent months, the fighting has spilled over into the capital.
The EPDP has accused the guerrillas of slaying at least 40 other party activists since the government and the rebels signed a cease-fire in 2002.
Police suspected the slaying in Colombo was linked to this feud.
Separately, in eastern Batticaloa, another Tamil man was found shot dead. Police had not yet identified the victim, but suspected that slaying also was connected to fighting between the rebel factions.
On Sunday, the bodies of two other suspected rebels were found riddled with bullets elsewhere in the Sri Lankan capital, hours before another man was found shot dead by suspected rebels on the east.
The Tigers began fighting in 1983 to carve out an independent homeland for the island's ethnic Tamil minority, who claim discrimination by the majority Sinhalese.
Nearly 65,000 people were killed before the 2002 cease-fire.
Peace talks have been stalled since April 2003.
