Some demonstrators in Geneva on Saturday condemned Israel
Washington has confirmed it will boycott a UN forum on racism in Geneva next week because of differences over Israel and the right to free speech.
The state department said the proposed text of the conference's guiding document remained unacceptable despite having been amended significantly.
The US and Israel quit a similar forum in Durban in 2001 when its draft document likened Zionism to racism.
Current language about "incitement to religious hatred" also alarms the US.
The five-day Durban Review Conference is due to open on Monday.
EU diplomats were still consulting on Saturday on whether to attend the conference. Canada and Israel said earlier that they would not attend.
Iranian President Mahmoud Ahmadinejad, who has stirred outrage by previously calling the Holocaust of the Jews a "myth", is the only prominent head of state so far scheduled to attend.
The state department said it was "with regret" that the US had decided to boycott the conference.
"The text still contains language that reaffirms
the Durban Declaration and Programme of Action [DDPA] from 2001, which the United States has long said it is unable to support," it said in a statement.
"Its inclusion in the review conference document has the same effect as inserting that original text into the current document and re-adopting it.
"The DDPA singles out one particular conflict and prejudges key issues that can only be resolved in negotiations between the Israelis and Palestinians.
"The United States also has serious concerns with relatively new additions to the text regarding 'incitement', that run counter to the US commitment to unfettered free speech."
Internal debate has raged in the US for weeks on whether to attend, the Associated Press news agency reports from Washington.
Pro-Israel groups vehemently opposed participation while human rights advocates and organisations like TransAfrica and members of the Congressional Black Caucus thought it was important to attend.
Immediately after the announcement, Democratic Congresswoman Barbara Lee, who heads the black caucus in Congress, said the group was "deeply dismayed" by the boycott.
"This decision is inconsistent with the administration's policy of engaging with those we agree with and those we disagree with..." she said.
"The US is making it more difficult for it to play a leadership role on UN Human Rights Council as it states it plans to do. This is a missed opportunity, plain and simple."