An aviation spokesperson confirmed a report in The Indian Express newspaper which said intelligence officials had uncovered a plot by individuals linked to al-Qaeda and the Pakistan-based Lashkar-e-Taiba group to hijack an Air India or Indian Airlines flight.

Air marshals

Al Jazeera's Prerna Suri, reporting from the capital, New Delhi, said air marshals had been deployed at certain flights in the South Asia region and a number of other security measures had been taken.

"Air security has been heightened across the country and passengers are being subjected to extra security checks until the end of the month.

"The authorities are looking into this intelligence alert very seriously indeed."

Indian media said the hijack threat was uncovered during the interrogation of Amjad Khwaja, belonging to Harkat-ul-Jihad-al-Islami, a group involved in numerous attacks in India.

Khwaja was arrested in the southern Indian city of Chennai last week and was being questioned by Indian police.