In the aftermath of Israel's 2008-2009 intervention into the Gaza Strip, Susan E. Rice, the U.S. ambassador to the United Nations, led a vigorous campaign to stymie an independent U.N. investigation into possible war crimes, while using the prospect of such a probe as leverage to pressure Israel to participate in a U.S.-backed Middle East peace process, according to previously undisclosed diplomatic cables provided by the anti-secrecy website WikiLeaks.