New Delhi, Nov 16 (IANS) Nuclear installations in the country have been put on high alert and security tightened as a precautionary step after intelligence agencies cited possible terror attacks, home ministry sources said Monday.

The alert comes after intelligence agencies discovered that David Coleman Headley, the Pakistan-born American national who is in US custody, had been to three states - Gujarat, Maharashtra and Uttar Pradesh - that have crucial nuclear installations.

Patrolling and security has been stepped up in six major nuclear energy plants in the states.

'It is a precautionary step. There is nothing specific but the states have been asked to tighten security, enhance vigil and patrolling in the vital nuclear facilities,' a home ministry official said.