Security at international airports in Mumbai, Hyderabad and Chennai was on Sunday put on maximum alert after the state police forces and the CISF were informed about a possible aircraft hijack attempt.

Mumbai Police on Saturday night received an e-mail, purportedly sent by a Hyderabad-based woman, who claimed to have overheard six men telling each other that “all 23 people have to split from here and board flights in three cities and hijack planes”.

CISF Director General O P Singh said the security apparatus at these airports has been put on “an enhanced alert and protocols have been stepped up.

“The e-mail could eventually turn out be a hoax but till investigations conclude all security drills to thwart a hijack- like scenario are being carried out at the three airports,” he said.

“The unidentified woman wrote in the e-mail that what she heard could be 'true or not' but she chose to inform the authorities as she felt it was her duty to do so as a citizen,” Singh said.

The contents of the e-mail were shared by Mumbai Police with all security and intelligence agencies on Saturday night itself and a meeting of all stakeholders at these airports was subsequently convened with the input being declared specific and actionable, officials said.

Special anti-sabotage sweeps are being carried out at the three airports since early Sunday and security agencies, including the CISF, were carrying out proper passenger checks, baggage scanning, pre-embarkation checks, secondary ladder point checking and patrols to thwart any bid to storm the airports.

The CISF has also pressed into service its sniffer dog squads and quick reaction commando teams for undertaking sanitisation drills at the airports, officials said, even as the airlines have been asked to remain extra vigilant.

At the Chennai airport, security has been strengthened at the domestic and international airports.However, flight traffic is unaffected by the enhanced security measures, officials said in Chennai.

Other airports in the country have also been sanitised and officials asked to remain vigilant, the CISF DG said.The police are probing the contents of the e-mail and trying to ascertain the identity of the sender and get in touch with the person.