India test fired its most advanced intermediate range ballistic missile Agni-III on Sunday but it developed a snag and fell into the sea off the coast of Orissa without hitting the target, defence sources said.

The launch of the nuclear-capable missile, designed to hit targets at a distance of 3,500 km, from the Integrated Test Range at Wheeler Island was 'successful' but its second stage did not separate and it fell into the sea, the sources said.

They said the missile went up vertically to a height of about 12 km before the snag developed. The sources attributed the problem to a 'design failure'.

Officially, there was no confirmation of any problem, with a spokesman confining himself to a terse statement that 'the missile took off successfully' at 11.03 hours IST. He said 'the flight performance' was being analysed by the mission team.

Sources in the Defence Research and Development Organisation, which developed the missile and launched it, said complete details of the test-firing would be known in 'a day or two'.

The surface-to-surface missile had blasted off from a fixed platform as Defence Minister Pranab Mukherjee and top defence scientists looked on. This was the first launch of the Agni-III, the most sophisticated product of the Integrated Guided Missile Development Programme that started in 1983.

The testing of the missile has been repeatedly put off since November 2004 for a variety of reasons, including once for technical problems.