Israeli boats have obstructed the path of a Libyan cargo ship en route to the Gaza Strip.
The ship was said to be carrying about 3,000 tonnes of goods for residents of the Strip in defiance of an Israeli sea and land blockade of the territory, reported dpa.
Monday's scheduled docking was the first attempt by a foreign government to break the blockade.
The Al-Marwa departed from the Libyan port of Zuara on Tuesday evening carrying food, medicines, blankets and powdered milk, Jamal Khoudary, a member of the Palestinian legislature and organiser against the Israeli blockade, said.
"The ship is safe and will help us since it is carrying food and medicine. There is no reason to stop it," Khoudari told the Jerusalem Post.
Ehud Olmert, Israel's prime minister and Ehud Barak, the defence minister, met on Sunday night to discuss the ship and decided not to consent to its docking in Gaza, officials said.
"A ship like that is capable of carrying weapons no less than what was on the Karine, a weapons boat that was seized," an Israeli security official told Maariv newspaper in reference to a vessel intercepted by the navy in 2002 and found to be transporting 50 tonnes of weaponry to Gaza.
"From our perspective, it is a hostile ship that left from an enemy country and we will treat it accordingly."
The unidentified official also said it had been a mistake to let in the boats carrying pro-Palestinian activists.
"We should have stopped those ships," he said.
Libyan officials have not commented on the latest incident.
Three boats manned by pro-Palestinian activists have arrived in the Gaza Strip from Cyprus since August in violation of the blockade, without drawing Israel into action. The boats contained some aid supplies.
Israeli officials said that they did not want to give the US-based Free Gaza advocacy group any publicity by stopping them.
But another Israeli official said of the Libyan boat: "We will treat this boat different than the earlier ones that were allowed into Gaza.
"Libya is a hostile state to Israel and what guarantees do we have that the boat is not carrying weapons and explosives for Hamas?"
Israel imposed the blockade of goods into the Gaza Strip, part of occupied Palestinian territories, last year to put pressure on Gaza's Hamas rulers.