Police detained 10 people for questioning overnight after a bus bomb near the Sri Lankan capital killed five.
Authorities strongly suspect LTTE's involvement in the blast, the Defence Ministry said on Saturday.
The bombing on Friday occurred on a busy highway in Nittambuwa town, 40 km northeast of Colombo. Thirty more passengers were wounded in the blast.
"Combined security operations during the night were carried out in the area and 10 people were detained for questioning," military spokesman Brig. Prasad Samarasinghe said.
"At least 2 kgs of explosives were used in the blast, and investigations ... Strongly link the blast with the terrorists," Samarasinghe said, referring to the Tamil Tiger rebels.
No formal charges have been lodged against any of the detainees, who remained in police custody today morning, he said.
There was no comment from the rebels and phone calls to the insurgents' northern headquarters in Kilinochchi rang unanswered on Saturday.
Bus driver Nimal Hettiarachi, 40, said that the blast struck the back of the bus which was carrying about 65 passengers.
He said four badly burned bodies were recovered soon after the explosion.
Only hours earlier, the air force had bombed the Chilawatte Tamil Tiger naval base in northeastern Mullaithivu district.