Somali Pirates who seized a German gas tanker in the Gulf of Aden are demanding $6 million for the vessel's release, sources told Deutsche Presse-Agentur dpa on Monday.

The demand has not been confirmed.

The ship with 13 crew members on board was seized on Thursday morning en route from Europe to the Far East.

The captain of the 3 500-ton ship had reportedly expressed fears for the safety of the crew - 12 Filipinos and one Indonesian - if the hijacking is not resolved peacefully.

The pirates on board the tanker contacted the Hamburg-based Bernhard Schulte ship management company Saturday, two days after seizing the vessel.

The 100-metre-long vessel belongs to MPC Steamship, a branch of a German investment group, a spokesperson for the company in Hamburg said.

According to a MPC spokesperson, the ship had passed through the Suez Canal and waited for a day to join a convoy under Indian naval protection as it passed through pirate-infested waters.

The Indians however were now able to prevent the pirate attacks, despite exchange of fire leaving two pirates and one crew member injured.

The vessel was then steered away to the Somali coast.