The Indian Air Force and the Central Industrial Security Force have stepped up security at Reliance Industries' oil refinery at Jamnagar following the sighting of an “illuminated object” in the skies over the plant.

It is suspected the object, which was spotted hovering over the refiner twice — on the evening of January 24 and again early morning on January 27 - could be an unmanned aerial vehicle (UAV) from across the border in Pakistan.

"While it is difficult to say anything immediately as investigations are still on, the ministries of home affairs and defence have put the concerned security agencies and authorities on high alert," a senior government official told HT seeking anonymity.

Jamnagar refinery, the largest in the world, is located close to Pakistan border.

Indian intelligence agencies had last year identified it has a potential target for an attack by Lashkar-e-Toiba operatives.

RIL pointed out as local forces are ill-equipped to deal with high-tech air-borne assaults, the government should "investigate the incident on top priority... and thwart any possible misadventure in the future".