President Barack Obama has lifted a US funding ban for groups providing abortion services abroad, reversing a policy of his predecessor, George Bush.
The policy known as the “global gag rule” had stopped US government money going to groups which perform or provide information about abortion.
Health groups had complained of being badly hit. The US is a key backer of family planning programmes globally.
Anti-abortionists have criticised the move to lift the ban.
Mr Obama’s move has implications for hundreds of aid agencies.
Observers say organisations working in the world’s poorest nations – places where maternal mortality and infant death are high – have faced a tough choice: either sign the gag rule and be silenced on abortion, or refuse and lose millions of dollars in US aid.
The issue of abortion services remains controversial in the US. The BBC’s Richard Lister in Washington says this may be why President Obama signed the order with so little fanfare.
Earlier on Friday, US regulators cleared the way for the world’s first study on human embryonic stem cell therapy.
While the decision of the US Food and Drug Administration is independent of White House control, Mr Obama is widely expected to adopt a more pragmatic and science-oriented approach to stem cell research.
A spokesman for the International Planned Parenthood Federation (IPPF) earlier told the BBC that under the Bush administration, the organisation had lost more than $100m (Ã‚Â£73m) in funding, affecting its services across 176 countries.
“It’s had a massive impact on delivery of services of family planning across the globe, but in particular in Africa,” said Paul Bell of the IPPF.
“No money supplied by the US federal government can be used for abortion-related services. But this rule effectively gags foreign NGOs from talking about the issue if they accept US funding. It is not applied to US-based NGOs as it would be deemed unconstitutional.”
However, some conservative groups in the US say taxpayers’ money should not be used to pay for abortion or its promotion.
The Christian group Focus on the Family said lifting the ban on taxpayer funding of overseas abortions was not only contrary to the values of the American people but would only increase the number of abortions being performed.
“President Obama claims that he wants to reduce abortions,” Focus on the Family’s Ashley Horne told the BBC.
“However, you cannot reduce abortions by channelling more money to the abortion industry.”
The policy has become a see-saw issue between Republican and Democratic administrations.
Former President Bill Clinton, a Democrat, repealed the policy when he took office in 1993 and George W Bush reinstated it in 2001.
The ruling is also known as the Mexico City Policy, because it was first introduced at a UN conference there in 1984 by former Republican President Ronald Reagan.