A consignment of over 100 tonnes of explosives meant for use by the Border Road Organisation for road construction in Afghanistan has gone missing from a merchant ship off the coast of Mumbai, sending alarm bells in security establishments.

The captain and six crew of the Iran-bound ship have been detained and questioned by authorities to ascertain how the explosives went missing after the vessel had set sail from Mumbai on December 22.

The explosives were meant for blasting rocks and mountainsides for the highway being built by BRO to link Delaram with Kanadhar in Afghanistan.

Officials said the ship, after sailing from Mumbai for the Iranian port of Bandar Abbas where the consignment was to be offloaded to be taken to the project site, had gone missing just 10 to 15 nautical miles off Mumbai.

The Navy and Coast Guard located the vessel just off the Mumbai coast on December 23 and towed it back under escort. The captain claimed that the explosives, carried in five to six containers, had sunk in the sea in rough weather, officials said.

A search has been launched for the shipping agent who had booked the explosives.

A high-level team of experts from intelligence agencies, state police, customs, Coast Guard, Navy and the Army has been set up by Union Home Ministry to probe the incident, officials in New Delhi said.

Samsu Sheroff, director of Unimarine Ltd, the shipping company, said about six hours after the ship had sailed, it encountered very choppy seas and the master of the ship reported that one of the containers in the deck been loosened and might fall in the sea.

He said the master again sent a message to the owner of the ship on December 23, saying one container had already been lost.

When the ship was asked on December 24 to return to Indian territory, the master turned around to come to Mumbai and 'in the bargain other five containers on board were lost. So, totally all the cargoes meant for Bandar Abbas from where that was to go Afghanistan for the BRO (were lost)', Sheroff said.

Maintaining that the cargo had been lost in the sea, he said it must be lying on the sea bed.

All the crew members of the ship had been take into custody, defence ministry sources in Delhi said adding security agencies were looking at the missing of the cargo from all angles.