Freedom Flotilla of three cargo ships and five passenger ships plans to attempt to break the siege of Gaza, and the first ship has already set sail, Press TV reported.
Tel Aviv has imposed a land, air, and sea blockade on the Gaza Strip since mid-June 2007, when the Palestinian resistance movement Hamas gained control of the territory.
The restrictions have deprived Gaza's 1.5 million Palestinians of fuel, food, and other necessities.
The Freedom Flotilla convoy carries 5,000 tons of construction materials, medical equipment, and school supplies, as well as around 600 people from 40 countries.
"This is a provocation and a breach of Israeli law," AFP quoted Israeli Foreign Ministry official Naor Gilon as saying on Monday.
Addressing a meeting of foreign ambassadors, he said, "Israel has no intention of allowing the flotilla to enter Gaza."
The international human rights organization the Free Gaza Movement is coordinating numerous pro-Palestinian groups in the Freedom Flotilla project.
The Rachel Corrie, a Freedom Flotilla ship named after a US peace activist who was killed by an Israeli army bulldozer in Gaza in 2003, has already set sail.