India has tightened airport security across the country after Western security services warned of a possible hijack attempt by terrorists.
India's civil aviation ministry has been warned that flights run by state-run Air India and other private carriers could be targeted by Islamist groups aligned to Al-Qaeda or the Pakistan-based Lashkar-e-Taiba rebel group.
"We have intelligence inputs that there could be a hijack attempt of Indian planes," said U K Bansal, senior home ministry official in charge of internal security.
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"We suspect that there can be an attempt to target one of our airlines, especially those which fly abroad."
New security measures including additional checks on baggage and travellers at airports and the deployment of sky marshals on planes were being put in place, a statement from the civil aviation ministry said.
Fears of 'provocative act'
The alert came after US Defence Secretary Robert Gates warned on Wednesday that Islamist South Asian militant groups could trigger a war between Pakistan and India through a "provocative act".
He also said that the US would continue to share intelligence to prevent an attack.
Tensions are running high between Pakistan and India in the wake of the November 2008 Mumbai attacks that New Delhi says were planned and executed by the LeT.
"We have alerted the ministry of civil aviation and bureau of civil aviation security and tightened security in all airports in the country," Bansal added.
The alert warns of flights from India or originating in countries neighbouring India - Bangladesh, Bhutan, Myanmar, Nepal or Sri Lanka - being specific targets.
A civil aviation ministry spokeswoman Moushumi Chakravarty confirmed the alert had been received.
Islamic insurgency "The information has been passed on to airport authorities and airline offices," she told news agency AFP.
The last hijacking in India occurred on Christmas Eve in 1999 when Islamic rebels seized an Indian Airlines plane travelling from Nepal to New Delhi and forced it to land in the then-Taliban stronghold of Kandahar in southern Afghanistan.
One passenger was stabbed to death by the hijackers before New Delhi agreed to release four Islamic militants in exchange for the 167 passengers and crew.
India has been battling an Islamic insurgency in its Muslim-majority region of Kashmir.
Prominent rebel groups fighting Indian troops in the disputed region include the LeT and the Jaish-e-Mohammed, founded by one of the militants freed in return for the Indian plane hostages.
