The rebel Liberation Tigers of Tamil Eelam set off the mine, planted near an electricity transformer, targetting a bus taking constables home on leave, a ministry spokesman said.
"Six policemen were killed and some more were wounded when the LTTE detonated a Claymore mine," the spokesman told reporters in Colombo.
Security forces on January 19 captured the main Tiger stronghold of Vakarai town where they maintained a de facto separate state for over 10 years.
