New Delhi: International airports at Mumbai, Chennai and Hyderabad have been put on high alert following threats of a hijack attempt.

Not only a full anti-hijack drill has been started and but also the National Security Guards (NSGs) have been put on stand-by.

As per reports, the alert was issued after a woman sent an email to a senior police officer in Mumbai on Saturday. In the e-mail she said that she had overheard six men at a restaurant, discussing simultaneous hijack of flights from the three above mentioned airports on Sunday.

The Mumbai Police informed the Central Industrial Security Force (CISF) as it is in-charge of security at the country's airports. At entry gates and parking lots, security is increased and counter-terrorism teams have been put in place.

Sniffer dog squads and quick reaction teams are pressed into service and airlines have been asked to remain extra vigilant.

In turn, airlines have advised passengers to avoid last-minute check-ins and they have also been advised to cooperate with the security personnel at the airports.

In January 2015, after a similar hijack threat, the CISF had reviewed its procedures and anti-hijack drills were held at airports and communication lines.

The intelligence agencies, at that time had spoken of a hijack attempt on an Air India flight to Afghanistan's Kabul.