Activists have condemned as an “assault on women's health”, a decision by Donald Trump to block US funding for health clinics around the world that provide abortion services.

One of the three executive orders Mr Trump signed on his first Monday morning as president, was to reinstate the so-called Mexico City Policy, a rule originally introduced by Ronald Reagan.

The rule, which was revoked by Barack Obama, forces NGOs to agree to “neither perform nor actively promote abortion as a method of family planning in other nations” as a prerequisite for federal funds. It does not matter if non-US funds are being used for the abortions.

Activists say the rule threatens to undermine the viability of countless groups that provide healthcare, including contraception and abortion services, to millions of women in the developing world. Campaigners had said ahead of Mr Trump’s inauguration, they feared he would reintroduce the policy as a gift to Vice President Mike Pence, known for his staunch opposition to abortion rights.

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The rule, first introduced in 1984, was named for the location of the UN conference on population where it was announced.

Groups that support abortion rights have long opposed the policy and urged politicians not to back. Republican and Democratic presidents have taken turns to impose and rescind the rule.

Bill Clinton revoked it in January 1993 upon taking office, and George W Bush reinstated it when he assuaged the presidency eight years later. Barack Obama most recently rescinded it again in 2009.

Mr Clinton and Mr Bush signed their orders on 22 January, the anniversary of the 1973 landmark Roe v Wade decision.