The Sri Lankan Air Force said it bombed a hideout of senior Tamil rebel leaders on Thursday in the northern part of the country and captured a rebel-controlled area, killing at least 18 rebels, as an ineffective ceasefire was officially terminated.
The rebels were killed in three separate incidents as troops advanced into the Pallekuli area of the Mannar district, 330 km north of the capital, hours before the truce ended.
But details of the clashes were announced only after the nominal truce ended, a military spokesman said.
Heavy fighting has been reported in the area over the past four days and details of the fighting are gradually emerging.
Tamil rebels said that in the same region they forced advancing troops to abandon their movement after they were lured into a minefield.
Troops were advancing from different directions into the rebel-controlled areas, but were facing stiff resistance from the rebels.
Thursday morning air force jets carried out the airstrike in the Jayapuram area of Kilinochchi, 320 km north of Colombo, and the pilots confirmed they had hit their target, the air force said.
There was no immediate reaction from the Tamil rebels, but a pro-rebel website said the air force had bombed a civilian area in the same district, injuring seven civilians.
Tamilnet said a workshop near a school was bombed in the suburbs of Kilinochchi, the rebel heartland where their political headquarters is located.
There was no immediate independent confirmation about the incident, but residents earlier said that with the government deciding to pull out from the truce at midnight Wednesday, they feared more airstrikes in the region.
Rebels are imposing strict restrictions on civilians in areas they control in an attempt to prevent information regarding rebel movements and locations from reaching security forces.
The airstrike came a day after a mine blast tore through a passenger bus in southeast Sri Lanka, killing 27 civilians. The government blamed Tamil separatist rebels and said the perpetrators also opened fire after the explosion, killing six farmers.
The absence of a truce with the rebels has caused concern among the public as they fear more violence, but the government defended its decision, saying that during the truce, the rebels had carried out similar attacks.
The 6-year-old peace accord had been virtually ignored since rebels renewed attacks on government forces in December 2005 and the military responded by launching a series of operations against them.
The country's ethnic conflict began in 1983 and has claimed more than 75,000 lives.
The rebels are fighting for a separate homeland for the Tamil minority in northern and eastern Sri Lanka.