Eleven schoolchildren are among at least 18 people killed in a bomb attack on a bus in north-western Sri Lanka, the Roman Catholic church says.
Bishop Rayappu Joseph told the BBC that the bus travelling near the town of Mannar was hit by a claymore mine in an area controlled by the Tamil Tigers.
The pro-rebel Tamilnet website said it was carried out by the Sri Lankan army.
The army, which pulled out of a ceasefire earlier this month, denies any involvement.
The incident comes as the army says it is making more advances in Tiger-controlled territory.
Bishop Joseph said victims of the attack had been taken to Pallamadu hospital, south-west of Mannar.
The bishop said that the bus was hit about 1km (0.6 miles) away from Madu church - about 3km from the front line which divides the rebels from the army.
He said it was travelling to the village of Pallamadu when it came under attack.
The head of the rebels' peace secretariat, S Pulithevan, told the BBC that the children were returning from a sports meeting.
He said that seven adults, including teachers, were among the dead and blamed the Sri Lankan military for planting a roadside bomb.
Dr Vettinathan, a local medical official told the BBC News website: "There are about 20 casualties (in hospital)...four or five of the victims are in a serious condition. There is one doctor in the hospital."
The incident came as the military said that it had captured territory in the north-west and killed 22 Tamil Tigers.
The government says it can defeat the rebels in the battlefield
Military spokesman Brig Udaya Nanayakkara said that the Tigers were being "hammered on all fronts" and were trying to tarnish the image of the military and the government.
The army said that more than 40 rebels and three soldiers were killed on Monday.
The BBC's Roland Buerk says that the heaviest fighting is taking place on front line around Mannar.
On Tuesday soldiers pushed across the defences there, according to the military. The military said that it had captured small areas of land fortified with more than a dozen bunkers in two separate battles.
Our correspondent says that the government refuses to allow reporters into the conflict areas and the casualty figures cannot be independently verified.
The civil war has intensified in Sri Lanka since earlier this month, when the government pulled out of a ceasefire with the rebels, who want an independent state.
The military is hoping to wipe out the Tigers by the end of this year.
President Mahinda Rajapaksa says he will also produce a political solution to resolve the Tamil minority's complaints of discrimination.