The military has denied it was involved in the bombing.
Udaya Nanayakkara, a military spokesman, said: "We don't operate in that area."
But the Sri Lankan government confirmed fighter jets were active on Friday over the north and that security forces had inflicted heavy losses on Tamil Tiger fighters in two days of fighting.
Three passengers were wounded and admitted to the Kilinochchi hospital, the statement from the separatist fighters said.
There has been an increase in violence since the government withdrew from a ceasefire agreement in January.
Friday's violence took place as the Tigers' mourned the death of Balasegaram Kandiah, a senior separatist leader who died of a heart attack at the age of 43 on Tuesday.
Gunbattles across the north of the island on Thursday killed 22 LTTE fighters and two soldiers, Nanayakkara said.
The Tamil Tigers have been fighting since 1983 for an independent homeland for minority ethnic Tamils, who have been marginalised for decades by governments dominated by the Sinhalese majority.
More than 70,000 people have been killed in the fighting.