Israel has stepped up its attempts to stop an aid ship breaking its blockade of Gaza, sending a letter to the UN and engaging Greece and Moldova in talks.
The Moldovan-flagged ship, Amalthea, chartered by a charity run by the son of Libyan leader Col Muammar Gaddafi, was due to leave the Greek port of Lavrio on Saturday.
Israel said it now believed the ship would not reach Gaza.
An Israeli raid on a Gaza-bound ship in May killed nine Turkish activists.
Israel insisted its troops were defending themselves but the raid sparked international condemnation. Israel recently eased its blockade, allowing in almost all consumer goods but maintaining a "blacklist" of some items.
Israel says its blockade of the Palestinian territory is needed to prevent the supply of weapons to the Hamas militant group which controls Gaza.
Israel has been engaged in intense diplomatic activity to prevent the Amalthea, renamed Hope for the mission, reaching Gaza.
A foreign ministry statement said that Foreign Minister Avigdor Lieberman had spoken with his Greek and Moldovan counterparts on the issue.
The statement said: "The foreign ministry believes that due to these talks, the ship will not reach Gaza".
Ministry officials quoted by the Israeli news source Haaretz said that if the ship did sail it would travel instead to the Egyptian port of el-Arish.
Israel also lobbied the UN to take action.
Israel's UN ambassador Gabriela Shalev said in a letter: "Israel calls upon the international community to exert its influence on the government of Libya to demonstrate responsibility and prevent the ship from departing to the Gaza Strip".
Ms Shalev also warned: "Israel reserves the right under international law to prevent this ship from violating the existing naval blockade on the Gaza Strip".
She said the motives of the operators were "questionable and provocative".
'Expressing solidarity'The Amalthea is being loaded with about 2,000 tonnes of food, cooking oil, medicines and pre-fabricated houses.
It has been chartered by the Gaddafi International Charity and Development Foundation. Its chairman is Saif al-Islam Gaddafi.
The organisation said the 92m (302ft) vessel would also carry "a number of supporters who are keen on expressing solidarity with the Palestinian people".
The BBC's Malcolm Brabant in Lavrio says the Libyans clearly believe the time is right to test Israel's resolve to maintain the naval blockade.
Charity director Yousef Sawani said: "We are doing what we can, this is our responsibility. If everyone says 'we will not allow this', nothing will happen and the people of Gaza will continue under starvation".
