The "Al Marwa" was approaching the Gaza coast when it was stopped by an Israeli navy vessel, said Gaza lawmaker Jamal Khoudary, who was in contact with the crew.

The Israeli navy crew ordered the Libyan ship via radio contact to turn back, said Israeli Foreign Ministry spokesman Yigal Palmor. He said the navy vessel did not use force.

It was not immediately clear where the Libyan ship was headed.

Gaza's borders have been largely sealed by Israel and Egypt since the Islamic militant Hamas group seized control by force in June 2007.

At times, restrictions were eased to allow the movement of medical patients, Muslim pilgrims, humanitarian supplies and a trickle of commercial goods. However, Israel re-imposed a tight closure Nov. 5, to force Hamas to halt rocket fire on Israeli border communities. The closure has led to shortages of many basic goods.

Since the summer, international activists have organized three trips from Cyprus to Gaza on smaller vessels. Israel did not intercept the activists' boats, which carried some medicine and other supplies.

The trip by the Libyan ship, loaded with 3,000 tons of food, powdered milk and blankets, marked the highest-profile attempt yet to break the blockade. Though the Libyan government hasn't commented, Khoudary said the delivery was organized by the Libyan Foreign Ministry.

The international community, including Arab countries, have not recognized the Hamas government. Nonetheless, there has been growing concern over the deteriorating humanitarian situation in Gaza.

Last week, Arab foreign ministers said in a joint statement in Cairo that their governments would send food and medicine to Gaza. They did not say specifically whether they would deliver the aid by sea or by land.

The foreign ministers said they would coordinate with Egypt to ensure the supplies enter Gaza, suggesting they would take the land route, rather than confronting Israelis at sea. Egypt and Gaza share a border.

On Monday morning, spectators, journalists and dozens of porters assembled in Gaza City's small port, awaiting the arrival of the Libyan ship. Five flatbed trucks pulled up, ready to load the cargo.

Khoudary said he was in touch with the Libyan vessel until about 6:30 a.m., when he lost contact. He said he reached the crew again 45 minutes later and was informed that Israel had blocked the passage.

"The civilian boat carrying only humanitarian supplies and food was turned away by an Israeli warship," Khoudary said.