New Delhi: Security of airports across the nation was stepped up on Sunday after intelligence agencies warned of a possible hijack attempt by militants on Delhi-Kabul flights.

"Security around all the airports have been strengthened and we have taken all the measures that are required in the wake of the alert from intelligence agencies," official sources told PTI.

All anti-hijacking measures have been put in place, they said, adding that passengers' checking has also been beefed up at some of the major airports, including Indira Gandhi International Airport in the national capital.

An alert was sounded after security agencies warned of a possible hijack attempt on flights running between Delhi and Kabul. The warning also mentions Air India airline, according to news report.

The security agencies have also reportedly alerted airlines operating on the route that the flights can be the target of the militants.

Instructions have been given to ensure proper security check of passengers, staff and cabin baggage once the boarding is complete.

The warning comes a day after a call threatening to blow up Air India office in Kolkata was made on Saturday.

The security at the Kolkata airport was increased after the threat call and air marshals were reportedly deployed.

Police is probing the incident and trying to ascertain whether it was a hoax call.

(With PTI Inputs)