Friday's decision by the US Supreme Court to strip the nation's constitutional protections for abortion, overturning the 50-year-old Roe v Wade judgment,  is a huge blow to women's human rights and gender equality, the UN human rights chief has said.

The decision was made in the specific case of Dobbs v Jackson Women's Health, and Michelle Bachelet said it represents a "major setback" for sexual and reproductive health across the US.

The historic decision returns all questions of legality and access to abortion to the individual states.

Earlier the UN sexual and reproductive health agency (UNFPA) and the World Health Organization (WHO) noted that 45 percent of all abortions around the world are unsafe, making the procedure a leading cause of maternal death.

The agencies said it was inevitable that more women will die, as restrictions by national or regional governments increase.

"Whether abortion is legal or not, it happens all too often. Data show that restricting access to abortion does not prevent people from seeking an abortion, it simply makes it more deadly," the UNFPA said.

According to the agencies' "State of World Population Report 2022," nearly half of all pregnancies worldwide are unintended, and over 60 percent of these may end in abortion.

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The UNFPA said it feared that more unsafe abortions will occur around the world if access becomes more restricted.

Bachelet said access to safe, legal and effective abortion is firmly rooted in international human rights law and is at the core of women and girls' autonomy, and ability to make their own choices about their bodies and lives, free of discrimination, violence and coercion.

This decision strips such autonomy from millions of women in the US, in particular those with low incomes and those belonging to racial and ethnic minorities, to the detriment of their fundamental rights, she added.

The rights chief highlighted that the decision came after more than 50 countries with previously restrictive laws have liberalised their abortion legislation over the past 25 years.

With the ruling, the US is regrettably moving away from this progressive trend, she said.

Meanwhile, the UN agency, UN Women, said the ability of women to control what happens to their own bodies, is also associated with the roles women are able to play in society, whether as a member of the family, the workforce, or government.

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The 1994 Programme of Action of the International Conference on Population and Development, signed by 179 countries including the US, recognised how deadly unsafe abortions are and urged all countries to provide post-abortion care to save lives, irrespective of the legal status of abortion.

The document – resulting from a high-level meeting in Cairo, Egypt – also highlighted that all people should be able to access quality information about their reproductive health and contraceptives.