“The ship was monitored and was intercepted in accordance with international law,” the military said in a statement, before the vessel, named Freedom for Gaza and carrying 12 people, was taken to the Israeli port of Ashdod.

“The (military) clarified to the ship’s passengers that they are violating the legal naval blockade and that any humanitarian merchandise can be transferred to Gaza through the Port of Ashdod,” the statement said.

The people on board were taken for “further inquiry.”

The organisers of the flotilla said the boat, which was carrying medical supplies, was intercepted in international waters.

“The demands of Ship to Gaza are that the ship with its crew and cargo will be returned to the site of the boarding, and that they will be allowed to go in peace through international and Palestinian waters in accordance to international law,” they said in a statement.

“This is a demand that the eleven years-long illegal and destructive blockade on Gaza will be lifted at last.”

Freedom was the second boat of the “Freedom Flotilla” to be intercepted en route to “break the blockade” on Gaza, organisers said.

Four boats left from Scandinavia in mid-May and stopped in some 28 ports along the way, with two remaining behind after a recent stop in the Italian port of Palermo.

On Sunday, the Israeli navy intercepted a Norwegian-flagged activist boat that was part of the flotilla.

Israel has fought three wars with Palestinian militants in Gaza since 2008 and says the blockade is necessary to keep them from obtaining weapons or materials that could be used for military purposes.

UN officials have called for the blockade to be lifted, citing deteriorating humanitarian conditions in the Palestinian enclave run by Islamist movement Hamas where 80 percent of the two million population are dependent on aid.