(CNN) -- Pirates hijacked a cargo ship Monday in the Indian Ocean, the European Union Naval Force Somalia said Tuesday.
At least four pirates, using two small boats and rocket-propelled grenades, boarded the MV Orna, a Panama-flagged merchant vessel owned by a United Arab Emirates company.
The number of crew members on board is unknown, but they are said to be cooperating and no damage has been reported, according to the naval force.
The attack happened about 400 nautical miles northeast of the Seychelles.
The European Union Naval Force Somalia is a multinational task force with the mission to escort merchant vessels carrying humanitarian aid of the World Food Program and vessels of the African Union Mission in Somalia.
The mission is "to protect vulnerable ships in the Gulf of Aden and Indian Ocean and to deter and disrupt piracy," it said.