According to a senior Israeli official in Jerusalem, Leahy began promoting the legislation in recent months after he was approached by voters in his home state of Vermont.

A few months ago, a group of pro-Palestinian protesters staged a rally across from Leahy's office, demanding that he denounce the killing by Shayetet 13 commandos of nine Turkish activists who were part of the flotilla to Gaza last May.

Leahy, who heads the Senate Appropriations Committee's sub-committee on foreign operations, was the principle sponsor of a 1997 bill prohibiting the United States from providing military assistance or funding to foreign military units suspected of human rights abuses or war crimes. The law also stipulates that the U.S. Defense Department screen foreign officers and soldiers who come to the United States for training for this purpose.

Leahy wants the new clause to become a part of the U.S. foreign assistance legislation for 2012, placing restrictions on military assistance to Israel, particularly to those three units.

Leahy says these units are responsible for harming innocent Palestinian civilians and that no system of investigation is in place to ensure that their members are not committing human rights violations. According to Leahy's proposal, U.S. military assistance to Israel would be subject to the same restrictions that apply to countries such as Egypt, Pakistan and Jordan.

The senior Israeli official said that the Israeli Embassy in Washington had been trying unsuccessfully now for some months to persuade Leahy to back down from the initiative.

Two weeks ago, during Barak's visit to Washington, Israel's ambassador to the United States, Michael Oren, asked Barak to meet with Leahy to dissuade him from promoting the legislation.