Somali pirates on Monday hijacked United Arab Emirates (UAE)-owned ship with unknown number of crew members northeast of the Seychelles, EU anti-piracy mission said.

EU Naval Force spokesman Paddy O'Kennedy said the midday seizure of the Panama-flagged MV Orna took place in the Indian Ocean, approximately 400 nautical miles northeast of the Seychelles. "The attack was launched from two attack skiffs, with pirates firing small arms and rocket propelled grenades at the merchant vessel. The vessel was stopped and boarded by at least four pirates," O'Kennedy said in a statement.

He said the crew is cooperating and that no damage is reported. The MV Orna is a bulk cargo vessel with a dead weight of 27,915 tonnes. "The number of crew onboard is unknown; MV Orna was not registered with MSCHOA or UKMTO," O'Kennedy said.

The pirates have intensified their action in the Indian Ocean and Gulf of Aden and most of hijackings end without casualties when a ransom has been paid, but often after several months of negotiations.

The Gulf of Aden, a body of water between Somalia and Yemen, is the main sea route between Europe and Asia. Tankers carrying Middle East oil through the Suez Canal must pass first through the Gulf of Aden.

About four percent of the world's daily oil supply is shipped through the gulf.

The attacks are being carried out by increasingly well- coordinated Somali gangs armed with automatic weapons and rocket- propelled grenades, maritime officials said.

The Horn of Africa nation has been without a functioning government since 1991, and remains one of the world's most violent and lawless countries.

Combined Task Force 150, a naval alliance dominated by the United States and based in the Gulf of Aden nation of Djibouti, is patrolling an area within the Gulf of Aden to help protect ships from pirates.