Sri Lanka's military says its fighter jets have destroyed a rebel base near the northern town of Kilinochchi where Tamil Tiger leaders were meeting.
The air strike comes a day after the ceasefire ended
But the pro-rebel TamilNet website said the bombs hit a civilian area, wounding seven people and damaging nine houses.
The conflicting claims could not be independently verified.
Meanwhile, rights group Amnesty International says it is gravely concerned at the end of ceasefire between the government and rebels.
"Sri Lanka Air Force fighter jets targeted a Tamil Tiger senior leaders' gathering at Jayapoor in Kilinochchi," news agency AFP reported, quoting from a defence ministry statement.
"Pilots confirmed that the location was completely destroyed," it added.
But the TamilNet website said the planes "bombed a civilian area with a mechanic workshop" and that Tamil Tiger rebels responded with anti-aircraft fire.
The air strike comes a day after Colombo ended a 2002 ceasefire with the rebels.
For the past couple of years, the truce - brokered by Norwegian monitors - remained only on paper.
The terms of the deal were repeatedly violated by both the government as well as the rebels.
Officials say that a total of 33 people died during and after the bombing of a bus in the south-east of the country on Wednesday.
Witnesses say that suspected rebels shot most of the passengers who survived the blast as they tried to flee the scene of the attack. At least 60 people were injured.
The army says that the attackers retreated into the bush after the bombing and shootings, killing six farmers they met along the way.
Meanwhile, the UK-based rights group Amnesty International says the end of the ceasefire will lead to a dramatic rise in hostilities in the country.
In a statement, Amnesty International said the end of the truce would also increase indiscriminate attacks against the civilian population.
It called on both the Sri Lankan government and Tamil Tiger rebels to comply with their legal obligation to protect civilians.
It also urged the international community to establish an independent monitoring presence in Sri Lanka.
The government gave notice two weeks ago it was pulling out of the 2002 ceasefire agreement.
It said the rebels - who are fighting for an independent state in the north and east - used the peace pact to rearm and regroup. It now says it aims to crush them by the end of this year.
The rebels have said they are ready to fight.
There were two bomb attacks on Wednesday, when the government formally ended the ceasefire with rebels.
At least 26 people were killed and more than 60 injured in one attack on a packed bus, the army said.