The suspected hijacking of an Alliance Air plane on Saturday morning was a mock exercise, senior officials in India's anti-hijack agencies told rediff.com.

The Alliance Airways Raipur-Nagpur-Delhi flight sent out a hijack signal about 20 minutes before landing at the Indira Gandhi International Airport in New Delhi.

The aircraft was immediately surrounded by Central Industrial Security Force commandos.

Deputy Managing Director of Indian Airlines V Kashyap told rediff.com that the plane had 127 passengers and eight crew members, including the two pilots.

The plane's scheduled time of landing in New Delhi was 1140 IST, but it was delayed by around 25 minutes.

Civil Aviation Secretary K Roy Paul said the exercise was carried out by various agencies involved in anti-hijack operations to test their preparedness.

A senior officer involved in the exercise said the response of the agencies "seemed appreciable," but a "detailed analysis would be undertaken" later.

A few weeks back a hijack alarm went off a New Delhi-Srinagar flight due to malfunctioning of the hijack switch. It led to a major scare and mobilisation of emergency measures.