The unidentified assailants of a Navibulgar bulker have steered the hijacked vessel close to Somalia's Puntland coast, under the constant watch of international navy vessels.

“Demands by the hijackers remain unknown,” EU naval force EUNAVFOR said in a statement on Tuesday updating on the situation of the 41,600-dwt Ruen (built 2016).

One of the ship's Bulgarian seafarers was released the day before for medical reasons.

The incident, which is believed to represent the first case of Somali piracy in years, has seen the vessel boarded on 14 December by a group of six people as it was sailing 700 nautical miles (1,300 km) off Somalia.

The Malta-flagged vessel was en route from Gwangyang in South Korea with a cargo of metals and 18 seafarers on board — eight Bulgarian citizens, nine from Myanmar and one from Angola.

The seafarers initially managed to lock themselves up in the citadel. Hours later, however, “the pirates managed to break into the citadel and extracted the crew,” EUNAVFOR said.

As of Tuesday afternoon, the Ruen moved between Somalia's Eyl and Xaafun peninsulas. At 1400 GMT, vessel trackers showed the ship about 5 km from the coast.

The Bulgarian crew member, who was allowed by the pirates to leave the ship, was transferred for medical treatment to the Kochi — the Indian navy vessel shadowing the Ruen.

The other war ship closely following the Ruen was EUNAVFOR's Victoria.

The Victoria “temporarily left the area for logistic reasons in the afternoon of 19 December,” EUNAVFOR said.

However, EUNAVFOR assured that the Ruen remained under continuously monitoring, in close collaboration with Somali federal authorities.

Navibulgar itself has made no public statement since its vessel was abducted five days ago.

The Bulgarian government has officially said it considers the Ruen as a piracy victim, most probably by Somalis.

The country’s Prime Minister Nikolay Denkov said on Sunday he was expecting ransom negotiations to begin soon.