Franco Frattini said no ransom money had been paid; the release was the result of collaboration between the Italian and Somali authorities.

The 75m (250ft) tugboat with its crew of 10 Italians, five Romanians and one Croat was towing two barges when it was seized in the Gulf of Aden in April.

It is now on its way to Djibouti, accompanied by naval vessels.

Mr Frattini expressed his satisfaction at the positive resolution of the affair and the release of the Italian citizens on board.

Their release was the result of a long process involving contact with the Somali government, the collaboration of the authorities in the semi-autonomous Puntland region, and the work of the Italian intelligence services, he said.

Somalia's UN-backed government is battling Islamist insurgents and controls only a small part of the country.

There has been no effective central government since 1991 and the lack of law and order has led to the dramatic rise in piracy in one of the world's busiest shipping lanes in recent years.