Sri Lankan government commandos killed six civilians including two children with a roadside mine inside the Tamil Tiger-held north of the island, the rebels said on Tuesday.
Monday night's attack, which took place in the Puliyankulam area, also injured four others, the Liberation Tigers of Tamil Eelam (LTTE) said in a statement, two of which were children.
There was no immediate comment from the Sri Lanka defence ministry, which does not comment on operations of its special forces.
All the victims were from three families and the injured have been admitted to the Mullaittivu hospital in the rebel-controlled northern area.
The LTTE blamed the army's "Deep Penetration Unit" for setting off the fragmentation mine as the families, which had squeezed into one old car, drove home from a religious ceremony.
"There could have been no doubt in the attacker's mind that the vehicle belonged to civilians," the statement said.
In May, the rebels accused government commandos of setting off two similar mines killing 19 people inside the guerrilla-held areas in the north.
Both sides in the conflict regularly accuse each other of targeting civilians.
Independent verification of casualty figures are impossible as the defence ministry bars media, aid workers and rights groups from travelling to frontline areas or crossing into rebel-held territory.
Fighting in the north has escalated since the government pulled out of a six-year Norwegian-brokered ceasefire in January.
The LTTE has been fighting to carve out a separate Tamil state in the ethnic Sinhalese-majority island since 1972. Tens of thousands have died on both sides of the conflict.