NEW DELHI, Aug 14 — With the threat of terrorist attacks looming large on the eve of Independence Day, especially in the wake of open threat by the Hizbul Mujahideen, the Centre has asked all state police chiefs to take all measures to ward off any untoward incident during the celebrations.

The Union Home Ministry, which took stock of the security arrangements made by various states, especially Jammu and Kashmir, Punjab, Gujarat and Rajasthan, asked the police in the states to ensure stringent security drill to foil any attack by militant groups acting at the behest of Pakistan.

Top Home Ministry officials reviewed the security arrangements made by the police in Delhi, where the main celebrations will take place at the historic Red Fort and will be participated by VVIPs and diplomats of other countries.

The intelligence agencies are keeping a close watch on militant activities in Jammu and Kashmir, Punjab and some southern states to ensure peaceful celebrations, Home Ministry sources said.

The airspace restrictions have been enforced in Delhi where the Prime Minister, Mr Atal Behari Vajpayee, will hoist the Tricolour and address the nation from the ramparts of the Red Fort. The airspace restrictions have been imposed in the wake of intelligence inputs that militants could use unmanned aerial vehicles to cause disturbances.

The air restrictions would be there till the Prime Minister addresses the nation and leaves the venue, the sources said.

Helicopters of the Indian Air Force would be pressed into service to maintain strict vigil in congested localities and areas around the walled city.

All manholes of sewerage in important areas like the Red Fort, railway stations, ISBT (Kashmiri Gate, Anand Vihar and Sarai Kale Khan), airports and other public places had been checked and constant vigil was being kept there, the sources said.

Besides threats from Kashmir and Punjab militants, intelligence reports said LTTE ultras could also create trouble, they said.