New Delhi: The first tests of a home-grown anti-ballistic missile system have been successful and the country expects it to be ready for military use in three years, a top missile scientist said yesterday.

India is also designing Agni IV, a new version of its longest-range ballistic missile, which will be capable of carrying a nuclear warhead and hit targets more than 5,000 kilometres away, V.K. Saraswat said.

The announcement came days after defence scientists said they had conducted a successful second test of an interceptor missile that destroyed a supersonic missile at an altitude of 15km on the country's east coast.

Nuclear weapons policy

India needed a missile shield as it had a policy not to use nuclear weapons unless it became a victim of a nuclear attack, Saraswat said, adding that this made India the fourth country after the US, Russia and Israel with such a capability.

"If, for instance, there is a missile taking off somewhere in our vicinity, I do not know whether it is coming with a nuclear tip or a conventional warhead," he told a news conference.

"It is essential you have a system which will first take on that kind of a threat. Because we have a ballistic missile defence system, a country which has a small arsenal will think twice before it ventures (to attack us)," he said in an apparent reference to Pakistan.

India's indigenous missile programme has built short- and long-range missiles, including one that can hit targets deep inside China.

The country has fought three wars with Pakistan and was on the brink of a fourth in 2002, and also fought a brief border war with China in 1962. Both China and Pakistan have their own missile arsenals that are capable of reaching almost all of India.

While China does not have a known anti-ballistic missile system, Indian scientists said its anti-satellite missile tested in January could easily be modified to meet this need.

"We have to conduct more flight trials to establish reliability and repeatability," Saraswat said. "I expect three years time for it to come to that level."

Asked if the new system would alter the military balance in the region, he said: "It is a defensive posture of our country, not an offensive posture. It doesn't alter the balance. It is just my capability to defend myself."