A Maltese-registered vessel has arrived in a Greek port after the owners alleged that a group of aid activists had tried to hijack it to take aid to Gaza, police said.

Ionian Bridge Shipping Management also denied that British aid workers had been held captive by the crew of the Strofades IV, which was transporting mainly vehicles.

Police in the Greek port of Piraeus said the cargo vessel had docked with a crew of 16 to 17 passengers, who were all "safe and sound."

The police said they were investigating what had happened, while an Ionian Bridge official, Maria Georgoulia, said a dozen activists had tried to storm the ship in the Libyan port of Derna on Thursday.

"They wanted to go to Egypt and then to Gaza," she said. "There is no contract between us and the activists, what they did was illegal."

She said that some 100 militants had gathered on the port at Derna on Wednesday wanting to board the Strofades IV.

"We called on the Libyan authorities to help us but finally seven Libyan police stayed on board the ship throughout the voyage without doing anything," Georgoulia added.

She said the crew had given food to the militants, "who put on a whole show on the deck, wearing lifebuoys and pretending to be in danger."

Georgoulia denied that the militants had been detained by the crew of the Strofades IV.

Ellie Merton, London liaison for the British group Road to Hope, said Thursday she thought the activists were being held by the ship's Greek captain after a dispute over money.

The British Foreign Office said, "We are aware of the incident at Derna Port in Libya and we have been in close contact with the organisers."

One of the Britons on board the Strofades IV was Tauqir Sharif, who was on the Mavi Marmara which was raided by Israeli commandos while en route to Gaza in May, resulting in the deaths of nine activists.