The exercises at Car Nicobar island, which is off-limits to civilians, involved a battalion-sized (1,000 men) combat force ferried by warships across the 900 kilometres (560 miles) from mainland India, they said.

"This is a week-long exercise to check the operational status of our base in Car Nicobar," a senior officer with the Integrated Services Command (Andaman's combined forces) said by telephone from Port Blair, the capital of the Andaman and Nicobar chain.

Lieutenant General Aditya Singh, chief commander of Andaman's combined defence forces, confirmed that the exercises were underway.

"This is an amphibious exercise and it is normal to bring in troops from various sources," Singh told AFP as others said the event also involved simulated protection against nuclear, biological and chemical attacks.

Car Nicobar, 150 nautical miles (278 kilometres) south of Port Blair and astride one of the world's busiest maritime routes, is India's most strategic airbase.

Last week, India held wargames in the desert near the Pakistan border and invited military observers from 30 countries. The Nicobar exercises by Andaman's integrated services however were being held in secrecy.

"We don't want outsiders prying here," said an airforce pilot involved in the operations in Nicobar, adding the wargames involved "attacks" by ground forces on the fortified island.

"The exercises have proved that the effects of the tsunami has been totally overcome and our assets in Car Nicobar are now fully operational," a defence ministry official in New Delhi said as the event held away from public gaze reached a climax Thursday.

Media reports in the past have suggested that some of India's nuclear assets are stored in the Andamans.

The 45-kilometre (28-mile) long island was one of the worst-hit Andaman islands when the December 26 tsunami smashed into the archipelago of more than 500 isles which stretches from Myanmar to Indonesia.

Some 110 air force personnel and family members died when the wall of water swamped the airbase, destroying aircraft on the ground or sweeping them out to sea.

A total of 1,899 people died on the Andamans, a majority on them in Car Nicobar, and 5,500 others remain officially listed as missing after waves as high as 70 feet (21 metres) struck.

"The airbase, which became operational the same day of the tsunamis, is now a multi-functional airbase which can operate any type of aircraft," Indian air force spokesman squadron leader Mahesh Upasini said.

"Fighter operations from Car Nicobar began in March itself," he added as other military officals said India's deep penetration Sukhoi-30 fighters and its British-built Jaguar bomber jets were using the airbase along with helicopter operations.

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