Chandigarh (PTI): The army's third generation anti -tank guided missile project 'Nag' is nearing completion and it will undergo one more "user trial" before it is cleared for induction, a top defence scientist said on Tuesday.

"The army is happy with the Nag missile. The first phase of user trials were completed in November and December 2007 and the final trial of this project will take place this summer," DRDO Chief Controller Research and Development (Missile and Strategic systems) Dr V K Saraswat told reporters here.

'Nag' (cobra) is an all weather, top-attack, fire-and- forget anti-tank guided missile, the design work of which was started in 1988 and first tests in November 1990. It is one of five missile systems developed by the Defence Research and Development Organisation under the Integrated Guided Missile Development Programme.

Saraswat however said there was a "dire need" to equip the country against threats from land, sea and air by developing a ballistic missile system.

"It is a requirement as more than 31 countries have developed and designed ballistic missiles," he said adding that DRDO had started building technology to detect the flight of ballistic missiles and reach the combat zone in time.

Replying to a question on whether there was a refueling problem with the surface-to-air 'Prithvi' missile, he said the Army had been using it since 1994 and was "very happy" with its functional capabilities.

"Pirthvi missile can be fuelled anywhere though it is generally done in depots. But once this missile is fuelled, it has a life of 10 years," he said.