The United States has decided not to participate in a UN conference on racism in April unless the final document is changed to drop all references to Israel and the defamation of religion, a senior US official has said. The conference is a follow-up to the contentious 2001 conference in the South African city of Durban which was dominated by clashes over the Middle East and the legacy of slavery. The US and Israel walked out midway through that eight-day meeting over a draft resolution that singled out Israel for criticism and likened Zionism -- the movement to establish and maintain a Jewish state -- to racism. Israel and Canada have already announced that they will boycott the upcoming World Conference Against Racism in Geneva from April 20-25, known as Durban II, but President Barack Obama's administration decided to assess the negotiations before making a decision on US participation. Last week, the State Department sent two US representatives to Geneva, where the final document to be issued by conference participants at the end of the conference is being negotiated, the US officials said, speaking on condition of anonymity because an official announcement has not yet been made.