U.S. Secretary of State Hillary Clinton says she opposes plans by pro-Palestinian activists to again try to challenge Israel's sea blockade of the Gaza Strip.

Clinton said Thursday the planned flotilla was neither “necessary or useful” in trying to assist Palestinians living in Gaza and would only increase tensions. She said any ships entering Israeli waters would only serve to provoke the Israelis, who Clinton said have a right to defend themselves.

She noted that the Israeli government earlier this week approved delivery of materials to build 1,200 homes and 18 schools in Gaza under United Nations-run projects.

A group of 36 Americans has announced plans to sail aboard a U.S.-flagged vessel to Gaza to challenge the blockade. Several Turkish groups say they plan to set sail within days. The U.S. State Department earlier this week discouraged Americans from making the trip, saying that the Gaza coast is “dangerous and volatile” and that the Israelis had blocked previous attempts to enter Gaza by the sea.

A year ago, Israeli commandos killed nine Turkish activists, including one who also had U.S. citizenship, when they boarded a Turkish vessel that was part of a flotilla trying to break the Israeli blockade.