The head of the United Nations' Human Rights Council announced on Monday he had appointed a US judge to join a panel set up to look into alleged war crimes during Israel's military offensive in Gaza.
Israel has already dismissed the panel as a "kangaroo court" that is biased in advance against the Jewish state.
US judge Mary McGowan Davis will join Canadian academic William Schabas and former UN racism investigator Doudou Diene of Senegal on the Commission of Inquiry created in July at the request of Palestinians backed by Arab and Muslim states.
Schabas is to chair the three-member group, to the annoyance of Israel which has pointed to the Canadian's record as a strong critic of the Jewish state and its current political leadership.
The head of the 47-member Human Rights Council, Gabon's Baudelaire Ndong Ella, personally selected the Canadian from a list which diplomats said had contained several candidates with little or no such "baggage".
Lebanese-born lawyer Amal Alamuddin, better known as the fiancée of US film star George Clooney, was also initially approached to join Schabas' team but declined.
Her replacement, McGowan Davis, who had a 24-year career in the New York City criminal justice system as state Supreme Court judge and federal prosecutor, was involved in an earlier investigation of Israel and her appointment could also spark controversy.
Diene also has a record of sometimes fiercely criticizing Israel for its treatment of Palestinians and its own Arab citizens during the six years he spent as the UN special investigator on racism from 2002-2008.
The new panel is due to make its first report by next March.
It is meant to look into the behavior of both Israel and of Hamas, the Islamist movement that controls Gaza and calls in its founding constitution for the destruction of the Jewish state.
Hamas has welcomed the appointment of Schabas, who lives in Britain and teaches international law at Middlesex University.
Schabas told Reuters this month he was determined to put aside any views about "things that have gone on in the past".
His appointment drew condemnation from pro-Israeli groups in the United States and Europe as well as from Israel. Some officials and diplomats in Geneva who are themselves critical of Israel say privately he was not the best option.
McGowan Davis was a member and later chair of a UN committee of independent experts which followed up on the findings of an earlier fact-finding mission into Israel's three-week incursion into Gaza in December 2008 and January 2009.
That mission, headed by South African judge Richard Goldstone, produced a report which bore his name and was rejected by Israel and strongly criticized by the United States and some other countries as "one-sided".
Goldstone himself later disassociated himself from some of the report's conclusions, saying that later information provided by Israel had convinced him that they were wrong.
As during the 2008-2009 conflict, Israel says it launched its latest offensive on July 8 to stop regular missile attacks from Gaza against civilian targets on its territory by Hamas and allied fighters.
On Monday, Palestinian health officials said 2,122 people had been killed in Gaza in the past seven weeks, most of them civilians and including more than 400 children.
Israel says Hamas deliberately hides its weapons and fighters among ordinary civilians. It says 64 of its soldiers and four civilians have died in the latest Gaza conflict.