Defense officials favor forcefully blocking two boats which a group of U.S.-based activists plan to sail to Gaza to protest what they call "the Israeli siege on the Strip," Haaretz has learned.

According to the Foreign Ministry, Israel is within its rights to use force against the seafarers.

The subject of the Greek-flagged boats which the Free Gaza group said it would sail from Cyprus to Gaza this week prompted defense officials to hold a series of discussions; they said allowing the ships to reach the Gaza coastline could create a dangerous precedent. But the Israel Navy has not yet received any instructions on how to treat the vessels.

According to some officials, Hamas is keen to exploit the initiative by the activists - including Israeli professor and activist Jeff Halper - for its political needs, and could try to greet the seafarers with fishing boats.

The officials believe that Hamas views the drive as an opportunity to underscore the suffering of the civilian population because of Israel's policies. A position paper by the Foreign Ministry's legal department says Israel has the right to use force against the demonstrators as part of the Oslo Accords, which names Israel as responsible for Gaza's territorial waters.

An official in Jerusalem said the Foreign Ministry's paper means that security forces could detain the vessels upon entry to Gaza's territorial waters, arrest the passengers and haul the ship to Israel, where the detainees could be interrogated.

The organizers have reportedly raised almost $300,000 to finance the operation and recruited 60 people to sail on the ship. These include activists from several countries as well as journalists.

In conversations with their Israeli counterparts, Cypriot officials have expressed concerns about the boat departing from their shores, but say they can do nothing to prevent it. According to the information that has reached Israel, however, Cyprus is not the only point of departure under consideration; the ship might also sail from Turkey or Alexandria in Egypt.