COLOMBO, April 27 (Xinhua) -- Sri Lankan President Mahinda Rajapakse has ordered to beef up security in all key installations in the island after Thursday night's air raid scare caused by Tamil Tiger rebels, officials said Friday.

    Rajapakse, who is currently in the Caribbean island of Barbados, had issued directions to related authorities, his office said.

    On Thursday night the capital Colombo and the main Air Force base near the Colombo international airport were placed under a security alert after reports that Liberation Tigers of Tamil Eelam (LTTE) aircraft were spotted off the northwestern coast.

    Group Captain Ajantha Silva, the Air Force spokesman, said, "we were alerted by people in Puttalam (a town 134 km northwest of Colombo) that one or two suspicious aircraft were spotted in the sky. Our air defense system was put in action but there was no attack of any kind."

    The defense establishment ordered the switching off of the city lights and the airport was shut down for some 40 minutes, officials said.

    Several planes were diverted to the south Indian city of Chennai.

    The LTTE carried out its first ever air raid in the over three decade old conflict late March by dropping bombs at the main Sri Lanka Air Force base near the international airport.

    Then early this week they carried out a similar air raid in the precincts of the Air Force base in the northern Jaffna peninsula.

    The rebel air capability has added a new dimension to the island's long drawn out separatist armed conflict.

    The current violence has put the Norwegian-backed process of negotiations on the back burner.