Tigers and the military have been trading charges over civilian deaths in the conflict, which has intensified after a ceasefire ended earlier this year.
A blast went off in a passenger bus en route from Matale to Kandy in central Sri Lanka in the late afternoon, police spokesman Ranjith Gunasekera said.
The explosion killed two persons and at least 20 were injured, the security media centre said.
In the morning, a roadside bomb which peppered a passenger bus with shrapnel in Katubedde, south of the capital Colombo, killed 20 and injured more than 60 people.
Tamil Tiger separatists have been blamed for a series of bombings in the capital and other areas in recent weeks.
Also on Friday authorities said they found an unexploded roadside bomb in the capital.
On Wednesday a suspected Tamil Tiger bombed a rail track as a train was passing through a southern suburb of Colombo, injuring several passengers.
Residents who saw a man arriving with packages raised the alarm,