Angry Turks have mourned activists killed in Israel's seizure of a Gaza-bound aid ship.

Israel is seeking to deflect UN demands for an international inquiry by offering its own probe with outside observers.

A new potential crisis is looming in Israel's four-year blockade of the Gaza Strip, as Prime Minister Benjamin Netanyahu instructed the military to prevent another pro-Palestinian ship from reaching the territory.

"We will not permit the ship to enter Gaza," an official in his office quoted Mr Netanyahu as telling a forum of senior cabinet ministers. The crew of the MV Rachel Corrie say the ship will reach Gaza by Saturday.

Mr Netanyahu said attempts to persuade the vessel, named after an American woman killed by an Israeli bulldozer in Gaza in 2003, to dock at the Israeli port of Ashdod for inspection had been rejected. He also ordered Israeli forces to exercise "caution and politeness" in handling the ship so as to avoid harm to any passengers, an official said.

US President Barack Obama said Israel "has legitimate security concerns" about the Hamas-ruled Gaza Strip. He also said Israel's blockade was preventing Gaza's people from pursuing economic opportunities.