Abortion rights activists protest in front of the U.S. Supreme Court June 29, 2022 in Washington, DC. AFP
WHO chief Tedros Adhanom Ghebreyesus described the decision by the top US court to scrap half a century of constitutional protections for abortion rights as "a setback".
Conservative-led US states have moved swiftly, at least eight of them imposing immediate bans on abortion, many with exceptions only if a woman's life is in danger.
A similar number is expected to follow suit within weeks.
Speaking to reporters from the UN health agency's headquarters in Geneva, Tedros voiced alarm that a country as influential as the United States would move "many years backwards" on the issue.
"We had hoped that US would actually lead on this issue," he said.
"Many countries... may follow suit," he warned, stressing that "the global impact is also a concern".
Tedros insisted that "all women should have the right to choose when it comes to their bodies and health. Full stop."
But he insisted that the issue of access to safe abortion was about much more than the right to choose.
"Safe abortion is health care. It saves lives," he said.
"Restricting it drives women and girls towards unsafe abortions, resulting in complications, even death." he said.
"The evidence is irrefutable: limiting access to safe abortion costs lives and has a major impact, particularly on women from the poorest and most marginalised communities."
The WHO's chief scientist Soumya Swaminathan agreed.
"Having access to safe abortion is a life-saving measure," she told journalists.
Blocking access "is like denying someone a life-saving drug that you know... can save their life," she said.
And it in no way reduces the number of abortions performed, but instead "drives women into the hands of people who are there to exploit the situation, performing unsafe abortions.
"So it's unfortunate to see some countries actually going backwards," she said.
"We will see the impact. There is no doubt that you will start seeing increases in mortality, as well as in huge amounts of morbidity as a result of this decision."