By Olivia Le Poidevin

GENEVA (Reuters) - Funding cuts have hit aid organisations that help the world's most vulnerable women especially hard, with over half of those surveyed at risk of closure within six months, a report by the United Nations agency for women said on Tuesday.

Since U.S. President Donald Trump returned to office in January for a second term, his administration has cut billions of dollars in foreign assistance in a review that aimed to ensure programmes align with his "America First" foreign policy.

The United States was the world's biggest aid donor, and its action has been aggravated as other international donors have also reduced funding.

The UN Women report found the funding cuts had affected 90% of the 411 women-led and women's rights organisations it surveyed - with half projected to close within six months unless new cash becomes available.

"Many women's organisations are now being stretched to the brink. They are being asked to do more, with less," Sofia Calltorp, director of UN Women's Geneva office, told reporters.

She said the suspension of U.S. foreign aid, which is subject to review, has affected more than $40 million of the body's funding for projects, with a devastating impact on women and girls in crisis areas.

In Afghanistan, for instance, women and girls must walk for hours to access basic health services because some health facilities have been closed, Calltorp said.

Also in Ukraine, more than 70% of women's organisations reported major disruptions and many have suspended shelters, legal aid and trauma support for survivors of the conflict, she said.

As the United Nations marks 80 years since its creation, its Secretary-General Antonio Guterres last month announced an initiative to improve efficiency and cut costs.

(Reporting by Olivia Le Poidevin; editing by Barbara Lewis)