MUMBAI (AFP) - India's navy was put on high alert Thursday (Sep 22) in the city of Mumbai, an official said, after reports that four men dressed in black and carrying weapons were seen near a base.

Security has been strengthened at several naval facilities along the coast in and around India's financial capital, while officials investigate the reports.

"The navy is at a high state of alert in Mumbai and adjoining areas after receiving inputs regarding suspicious activity reported by school children," Navy spokesman Captain DK Sharma told AFP.

Sharma did not reveal the nature of the activity, but local media reported that the children had seen gunmen, their faces covered, near a naval facility at Uran, about 50km from Mumbai.

"We are taking utmost care and precautions," Mumbai police spokesperson Ashok Dudhe also told AFP.

Mumbai is particularly sensitive to security threats after gunmen, who arrived by sea, went on a three-day rampage in 2008 in the western city that left 166 people dead. India blamed the attacks on Pakistani militants.

India has also been on guard since militants raided an army base on Sunday near the defacto border that divides the northern Kashmir region with Pakistan, killing 18 soldiers.