Taking place about 150 km (95 miles) from the border with Pakistan in the Rajasthan desert, it involves more than 60,000 soldiers, 300 tanks and 160 aircraft.

The manoeuvres - a mock eight-day battle between "Red Land" and "Blue Land" - near the city of Jodphur also feature the surface-to-surface Prithvi missile being used by the army for the first time.

Indian military officials say there is no threat or provocation intended against neighbouring Pakistan, which has been notified about the exercises.

The Pakistanis protested when news of the Indian military plans first broke, and the issue was discussed during a series of talks in Delhi.

A similar large-scale Indian exercise in the late 1980s seriously exacerbated tensions with Pakistan and was believed by some observers to have brought the two countries to the brink of war.

Highly professional

BBC correspondent Daniel Lak in Delhi says the Indian army and other armed services are regarded as highly professional, thanks in large part to regular manoeuvres such as these.

Lt-Gen Khanna: War games more relevant than before

A senior Indian officer, Lieutenant-General G.M. Khanna, said the nuclear tests earlier this year meant the manoeuvres were now more necessary than before.

"If this conflict is escalated by Pakistan, alas, or we wish to escalate because of various reasons, the next level for the conflict to escalate is conventional. Therefore the relevance is there and it has been increased," he said.

Brigadier D.K. Babbar said soldiers were being trained in nuclear and chemical warfare but insisted the training was "not something new".