"The activity ended without exceptional events," a military statement said. "At this time the ship is being transferred to the port of Ashdod" along the coast of central Israel.

An activist group affiliated with the boat, the Al-Awda (The Return), said 22 people and a cargo of medical supplies were onboard.

A second boat that is part of the same group, the Swedish-flagged Freedom, is expected to arrive in the same area in the next couple days, according to the Freedom Flotilla Coalition.

Four boats left from Scandinavia in mid-May and stopped in some 28 ports along the way, the coalition said. Two boats remained behind after a recent stop in Palermo.

Shortly before the Al-Awda, a fishing boat, was intercepted, the coalition released a statement saying the Israeli navy was issuing warnings to it.

"The Israeli navy claims our ship is breaking international law and threatens that they will use 'any measures necessary' to stop us," it said.

"In fact, the only 'necessary measures' would be to end the blockade of Gaza and restore freedom of movement for all Palestinians."

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 and rights activists have called for the blockade to be lifted, citing deteriorating humanitarian conditions in the Palestinian enclave of two million people run by Islamist movement Hamas.