Three persons, including two Tamil Tiger rebels, were killed in a powerful blast in northern Sri Lanka on Tuesday morning.

The three men were blown up while rigging an explosive device in the northern Periyarkulam village in the district of Vavuniya, police said.

They said at least two people killed in the blast were believed to be members of the Liberation Tigers of Tamil Eelam.

The explosion caused extensive damages to a house.

Meanwhile, the number of people killed in Monday's blast near Colombo rose to eight with a police commando succumbing to his injuries, hospital sources said.

Another 38 remained in hospital.

Police stepped up security in the capital and ordered that every vehicle entering the city be searched for explosives.