"Agni-IV is still in the design stage, and so we cannot give a date for the trials to begin," said V. K. Sarswat, the head of India's strategic missile programme.

But when asked to confirm if the missile will have a range of 6,000 kilometres, he replied: "It will be that much."

New Delhi has already begun production of two variants of the Agni -- a 700-kilometre (434-mile) Agni-I and the 2,500-kilometre (1,550-mile) range Agni-II after flight-testing both the ballistic missiles numerous times since 1993.

India is also working on an Agni-III, a two-stage solid fuel missile which has a range of 4,000 kilometres (2,480 miles). But a test in April ended in failure.

Sarswat declined to give further details on the new project, but a senior defence source told AFP that the first trial for Agni IV was slated for 2010.

"We have a tentative window which is three years from now," said a top defence scientist who did not want to be named.

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