The number of political killings in Sri Lanka this year is nearing 200, international ceasefire monitors say.
Sunday's funeral procession for the latest victim - an army colonel
The Norwegian-led Sri Lanka Monitoring Mission urged the government and the Tamil Tiger rebels to work together to end the cycle of violence.
It said a ceasefire which came into effect in February 2002 was being gradually undermined.
The monitors sent sympathy to the family of the latest victim - an army spy chief shot dead on Sunday.
The monitors said political killings had claimed 190 lives since the start of the year.
"The killings have gradually undermined the ceasefire and resulted in mistrust and a bad atmosphere between the parties," the mission said in a statement.
More than 60,000 people have died since 1972 in the Tamil Tigers' campaign for autonomy in the north and east.
The latest victim was Col TM Meedin, who was shot in the head near his home in Kiribathgoda, a suburb of the capital, Colombo.
Four people are being questioned, police said.
Col Meedin commanded the First Military Intelligence Corps and was the second most senior military officer to be killed since the 2002 truce.
No-one has yet said they carried out the killing.