The crew and security guards included British, Estonian, Indian and Ukrainian nationals, Kumar said. The southern tip of India is close to major trading routesfrom Asia to Europe. Many cargo ships now travel with armed guards to deter pirates. Sri Lanka, close to Tuticorin, is a popular boarding point for private armed guards.
"At the moment the documents are still awaited," Kumar said. "We have to see how valid are the documents that they do produce towards their entry into Indian waters and carrying arms and ammunitions."
The Sierra Leone-flagged ship Seaman Guard Ohio belongs to Virginia-based AdvanFort, a maritime security firm that specializes in anti-piracy operations. AdvanFort and the US consulate in Chennai were not immediately available for comment.
Kumar said the ship was approached and detained on Friday night. He said Indian authorities had been assured they would receive documentation within an hour of the detention, but that 24 hours later the ship's master had still not produced them.
In February last year, two Indian fishermen were allegedly shot dead by two Italian marines serving as security guards on an Italian-flagged oil tanker off the Kerala coast. The marines are currently being prosecuted in India.
The incident highlighted the loosely-regulated practice of placing private and military armed guards on ships for protection against pirate attacks.
Pirate attacks cost billions of dollars every year - as much as $5.7-6.1 billion in 2012, according to The Oceans Beyond Piracy advocacy group.