The US has insisted abortion should not be recognised as a human right, at a review of progress 10 years after a major conference on women's rights.
Abortion has dominated the meeting on women's rights
The issue has dominated the opening proceedings of the UN session organised to re-affirm the world's commitment to the Beijing declaration.
The US has submitted amendments insisting that any new declaration did not create "the right to abortion".
The conference is also discussing Aids, sex trafficking and women's education.
UN Secretary General Kofi Annan told the conference: "Over this decade, we have seen tangible progress on many fronts.
BEIJING CONFERENCE: MAIN ISSUES
Violence against women
Increasing burden of poverty on women
Unequal access to education
Poor opportunities for advancement
Inequality in economic structures and policies
Inadequate protection of women's human rights
"Life expectancy and fertility rates have improved. More girls are enrolled in primary education. More women are earning an income than ever before.
But he added: "We have also seen new challenges emerge. Consider the trafficking of women and children - an odious but increasingly common practice. "Or the terrifying growth of HIV/Aids among women, especially young women."
The 150-page Beijing declaration called for governments to end gender discrimination in areas including education, health care, politics and employment.
It stated that women have the right to "decide freely and responsibly on matters related to their sexuality... free of coercion, discrimination and violence."
But attempts at the time to refer to abortion as a sexual right were dropped amid heated debate, and instead it was treated as a public health issue.
However, the Beijing conference's action plan did call for governments not to punish women who have undergone illegal abortions.
The US position at the current meeting reflects President George W Bush's tough stance against abortion.
That contrasts with his predecessor Bill Clinton, who was in the White House at the time of the Fourth World Conference on Women.
The US amendments were submitted last week ahead of the start of the two-week meeting at the UN's headquarters in New York on Monday.
Richard Grenell, the US spokesman at the UN, said: "We believe wholeheartedly that the Beijing document does not establish or guarantee a right for an abortion."
About 100 government delegations, including 80 ministers, and 6,000 activists, are involved in the Beijing declaration progress review.
Organisers of the meeting stressed that the fresh declaration being formulated was not a legally binding treaty and did not create any new human rights.