The Israeli navy had initially "prevented the ship from entering Gaza waters" and ordered the vessel to head for Egypt, but the crew failed to obey, the Haaretz newspaper quoted Israeli Defense Minister Ehud Barak as saying.
The Togo-flagged "Brotherhood Ship," carrying 50 metric tons of humanitarian aid for Gaza, was towed to the Israeli port of Ashdod. Nine people were on board the ship, including Lebanese, Palestinian and British nationals.
The Israel Defense Forces spokesman rejected media reports that the ship had been fired upon, saying that the Israeli soldiers had boarded the vessel without using their weapons.
The ship was sent by the Palestinian National Committee Against the Siege in cooperation with the U.S.-based Free Gaza Movement.