The United States Friday sharpened its warnings to activists planning a new attempt to break the Israeli naval blockade and deliver relief supplies to Palestinians in the Gaza strip.

The Obama administration says the United States is making diplomatic appeals to countries around the eastern Mediterranean, including Israel, to avoid a repeat of the deaths and injuries of last year's flotilla incident.

News reports say several hundred pro-Palestinian activists including a number of U.S. citizens intend to leave Greece in as many as 10 private vessels this coming weekend to deliver humanitarian goods to Gaza and commemorate the flotilla effort broken up by Israel on May 31st of last year.

U.S. Secretary of State Hillary Clinton says she opposes plans to again try to challenge Israel's sea blockade.

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.

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.