A United Nations conference on racism is threatened by a growing Western boycott over fears it will be used as a platform for vitriolic criticism of Israel.

The United States announced on Saturday it would stay away, citing "objectionable" language in a text prepared for the Geneva meeting which Iranian President Mahmoud Ahmadinejad will address on its opening today.

Australia and The Netherlands have joined Canada, Italy and Israel who have also said they will shun the meeting, which the United Nations organised to help heal the wounds of its last race summit, in South Africa in 2001.

The United States and Israel walked out of that conference after Arab states sought to define Zionism as racist.

Australia said it shared US concerns about the declaration for the follow-up conference, which omits explicit references to Israel and the Middle East but "reaffirms" a text adopted at the 2001 Durban summit which singled out the Jewish state.

"Regrettably, we cannot be confident that the Review Conference will not again be used as a platform to air offensive views, including anti-Semitic views," Australian Foreign Minister Stephen Smith said in a statement.

An Italian foreign ministry spokesman said it would not send a delegation unless there was a radical last-minute change to the Geneva document, which he said was "very unlikely".

Dutch Foreign Minister Maxime Verhagen said he would not attend, citing concerns Islamic states would use the UN forum to try to bar "incitement" to religious hatred or "defamation of religion" - a concept borne of the 2006 controversy over Danish cartoons of the Prophet Muhammad.

"Some countries that still have a long way to go in the human rights domain are misusing the summit to put religion above people's rights and to unnecessarily restrict freedom of speech," Mr Verhagen said in a statement.

He described the conference document as "unacceptable" and a "missed chance" to fight racism and discrimination.