Sri Lankan authorities say a suicide bomber set off a blast on a bus Saturday, killing herself and 15 passengers.
They blame Tamil Tiger rebels for the attack south of the capital, Colombo.
Police say the blast wounded a number of other passengers. A senior police official, Upul Ariyaratne, says local hospitals are treating 40 people.
The attack is similar to a powerful blast Friday on a passenger bus north of Colombo that killed at least five people.
The military also blames that attack on the Tamil Tigers. A rebel spokesman denies the group had any involvement in either attack.
Earlier Saturday, the military said Tamil Tiger rebels triggered a series of roadside bombs in the north, killing four soldiers and a civilian.
Authorities say the bombs exploded near a truck that was transporting soldiers in the northern district of Vavuniya.
On Friday, Sri Lankan warplanes conducted air raids against Tamil rebel positions in the north and east of the country for a fourth consecutive day.
Violence continues in Sri Lanka despite a 2002 truce between the government and Tamil rebels fighting for an independent homeland. More than three thousand people died in the conflict last year.
The fighting is blamed for the deaths of some 67,000 civilians, troops and rebels since 1983.
Some information for this report provided by AP, AFP and Reuters.