Airports in Delhi [Images], Bangalore and Chennai were on Wednesday night put on high security alert in the wake of intelligence inputs that terrorists of Pakistan or Afghanistan origin may strike these installations by this weekend ahead of the anniversary of demolition of Babri Masjid.

The Civil Aviation Bureau is understood to have sent out the alert to the three airports following intelligence reports that several suspected terrorists have infiltrated into the country to carry out strikes.

The security alert came a day after top officials of Civil Aviation Ministry, Air Force, Bureau of Civil Aviation Security and DGCA held a meeting in New Delhi to review the preparedness of 'different layers' of security apparatus and safety mechanism in major airports as well as in the airspace in the wake of intelligence inputs.

Authorities have received 'specific' information that terrorists were planning to attack airports on December three, four or five, sources said.

Keeping this in mind, sources said, 'ladder-point' (at the time of boarding the plane) security checks have been introduced.

Major airports across the country, especially those in the western region, have been on high alert and extra vigil for the past few days following the terror strikes in Mumbai.

Extra surveillance has been mounted in most of the airports, with additional CISF and police personnel being deployed to keep an eye around the terminal as well as the perimeter.

Sniffer dogs have been deployed in some airports, while watchers in plainclothes were also put on the job. Sky Marshals were being put on planes flying on sensitive routes, sources said.