Airline and government officials said the civilian airport, 23 miles north of the capital, was not damaged but was closed for several hours following the attack. Four commercial flights that were on their way to Colombo this morning were diverted to Chennai. The flights returned to Colombo when the airport re-opened.

The rebels dropped three bombs from an aircraft that landed near the base’s engineering section just before 1 am, the Defence Ministry said in a statement. The military said the bombs hit barracks and none of its aircraft was damaged. One bomb did not explode.

Hours later, Air Force fighter planes bombed Tamil-held areas in northern Wanni district, the Tigers said in a statement. There were no casualties, said the statement, adding civilian property and farm lands were destroyed in the attack.

“A light Tiger aircraft flew over the Air Force base and dropped explosives. There have been two explosions. At the same time, our air defences activated and there is a search operation going on,” said Air Force spokesman Group Captain Ajantha de Silva.

But rebel military spokesman Rasiah Ilanthiraiyan claimed that the attack was carried out by two aircraft. “A couple of aircraft of Tamil Eelam Air Force have launched an attack on a Sri Lankan military airfield and hangars of military aircraft,” he said by telephone. He said the aircraft had flown back to the Tigers’ northern stronghold after what he called a “successful mission”.

“It is not only pre-emptive, it is a measure to protect Tamil civilians from the genocidal aerial bombardments by Sri Lankan armed forces,” he said. “More attacks of the same nature will follow.” The rebels did not say what kind of aircraft was used, but a Western diplomat said the plane is believed to be a Czech-made Ziln Z-143, a single-propeller trainer that had been modified to carry bombs.

Sri Lanka President Mahinda Rajapakse held an emergency meeting with leaders of political parties to discuss the attack. The government condemned what it called a “cowardly” attack, which followed weeks of Air Force raids on rebel targets in the north and east, and said security forces were on high alert.

“It’s a threat to the entire region, not only to Sri Lanka... India especially must be vigilant of this,” Highways Minister Jeyaraj Fernandopulle told reporters. Heavily armed troops manning checkpoints between Colombo and the airport carried out stringent checks on vehicles.

The Tigers, who say they are fighting for an independent state for minority Tamils in the north and east, last attacked the airport in 2001, the year before a ceasefire deal which has since collapsed. In that attack, half of Sri Lankan Airlines’ fleet of planes was destroyed.

The rebels have since smuggled an estimated four light aircraft into the country in pieces and re-assembled them. They have long maintained an airstrip outside Kilinochchi. The Tigers also have a naval wing, the Sea Tigers.

A pro-rebel website www.tamilnet.com carried pictures of rebel leader Velupillai Prabhakaran standing with Tiger pilots. It also showed a single-propeller two-seater plane painted in army camouflage colours with four bombs attached to its underside.

Peter Hill, Sri Lankan Airlines’ chief executive officer, said all inbound and outbound commercial flights had been halted for several hours.

Sri Lankan Airlines resumed its services, but Cathay Pacific Airways said it had suspended flights to and from Colombo, while Pakistan’s PIA and Thai Airways had yet to decide whether to cancel flights scheduled for later in the week.