The crew and guards have not been able to satisfactorily explain why they had entered Indian waters, sources in defence agencies have said.
Semi-automatic weapons have been found on board the ship, but sources say, the crew has failed to produce the necessary documents required to carry such weapons.
The ship's Captain has reportedly told investigators that the guards belong to a company which provides armed escorts, especially to merchant vessels in pirate-infested areas of southern Indian Ocean as well as Gulf of Aden.
The vessel, registered in Sierra Leone (West Africa), has been towed to Tuticorin port, where investigations are on by the Indian Coast Guard, Indian Navy, Customs and intelligence agencies.
Usually, ships do not carry the number of weapons as MV Seaman Guard had on board, making it a matter of slight concern to Indian authorities.