Two Irish people are among a group of activists who have been taken against their will from a port in Libya towards Greek waters on a Greek-registered ship.
The ship had been chartered by the Road to Hope organisation to take aid to Gaza.
The ship had entered the Libyan port of Derna, where a dispute arose over payments to the captain.
The captain decided to sail from the port and, according to Road to Hope, ten people are being held on board against their will.
The UK Foreign Office in London says it understands the ship is heading for Greek waters.
Road to Hope has said that the Greek captain of the Strofades IV wanted to drop his passengers off in Greece.
