Israel is "very unlikely" to cooperate with a UN agency's probe into whether Israel and Hamas committed war crimes in the recent Gaza war, a government official said Wednesday.

Hamas, meanwhile, said it is ready to work with the investigators, to be led by Richard Goldstone, a South African judge who served as chief UN prosecutor of war crimes in Yugoslavia and Rwanda.

International and local human rights groups have said there is strong suspicion both sides violated the rules of war in three weeks of fighting early this year that followed years of cross-border conflict.

The groups have said Gaza's Hamas rulers should be investigated for firing rockets indiscriminately at Israeli civilians and for allegedly using Gaza civilians as human shields during the fighting that ended Jan. 18.

Investigators must also look at the Israeli military's practices, such as firing imprecise artillery and white phosphorous shells in densely populated Gaza, the groups have said.

On Tuesday, the New York-based Human Rights Watch urged both sides to cooperate with Goldstone, who is a member of the group's board. An impartial investigation is needed since neither Hamas nor Israel seems willing to conduct a thorough probe, the group wrote to U.S. Secretary of State Hillary Rodham Clinton.

Human Rights Watch noted that it has criticized the Human Rights Council in the past "for its exclusive focus on Israeli rights violations." However, Goldstone has the "experience and proven commitment to ensure that this inquiry will demonstrate the highest standards of impartiality," the group said.

The Israeli government official said Israel sent its response concerning cooperation to the UN agency a week ago. He spoke on condition and said he could not elaborate because it's not clear whether Goldstone has been briefed.

Israel's ambassador to UN organizations in Geneva said Tuesday Israel does not have faith in the UN Human Rights Council.

"(It's) not about Justice Goldstone. It has nothing to do with him," the Israeli envoy, Aharon Leshno Yaar, said. "It's clear to everybody who follows this council and the way that it treats Israel that justice cannot be the outcome of this mission."