Israeli and Greek officials say a ship carrying aid for Gaza is now heading for Egypt instead, following diplomatic intervention by the Israeli government.
They say the Amalthea, chartered by a Libyan charity, has set sail from the Greek port of Lavrion, carrying 2000 tonnes of food and medicine.
It is just over a month since nine Turkish citizens died in an Israeli raid on an aid flotilla heading to Gaza on a similar mission.
Organisers say the boat, with 12 crew and up to ten passengers on board, will head for Gaza, but would go to the Egyptian port of El Arish instead if banned from its their destination.
'We hope the Israelis will not ban the ship from entering the port of Gaza. If they decide to do so we have no means to object to that. This is a peaceful mission,' said Youssef Sawani, executive director of the charity organising the aid trip.
He says it is a purely humanitarian mission with the sole aim of delivering food and medicine to the people of Gaza.
'No one can dispute they are in urgent need because they have been under boycott, seige; you name it, they went through it because of the Israelis' actions.'
Israel earlier asked the United Nations to prevent the ship from breaking its blockade on the territory.
Israel's ambassador to the UN, Gabriela Shalev, says Israel also reserves the right to stop the ship from reaching Gaza.
Israel recently eased its blockade, but maintains a 'blacklist' of some items, including building materials, which it says could be used for military purposes. It also forbids the export of goods from Gaza.