The Kalma camp, near the town of Nyala in Darfur, shown here in a photo by the aid group Doctors Without Borders. The agency was one of 16 expelled from Darfur in March. (Voitek Asztabski/Medecins Sans Frontieres/Associated Press)

Actress Mia Farrow has been forced, for health reasons, to end her 12-day hunger strike to draw attention to the humanitarian crisis in the Darfur region of western Sudan.

British entrepreneur Richard Branson has taken over the fast for three days in a gesture of solidarity with Farrow, a human rights activist and UNICEF goodwill ambassador.

Farrow had been on a water-only diet from April 27 in what she called an "expression of outrage" at Sudanese President Omar Hassan al-Bashir's expulsion of aid agencies from Darfur.

She ended the fast on Friday on her doctor's orders.

Actors Mia Farrow and Michael Douglas greet each other between speeches at the 2007 Millennium Summit in Montreal. The event was aimed at promoting peace and reducing poverty around the world. (Ryan Remiorz/Canadian Press)

"I have been instructed by my doctor to stop my fast immediately due to health concerns including possible seizures," Farrow, 64, said on her website.

She expressed disappointment that she wasn't able to complete the hunger strike she had planned. "I am a very stubborn person and very determined. I had modified my goal from 21 days and really hoped I would reach my goal of fasting for 16 days, which is the number of aid agencies [expelled]," she told People magazine.

In the final hours, she couldn't stand up. "I got out of bed and went down to my knees. My muscles were aching," she said.

Farrow asked Branson to take over for her. The founder of the Virgin Group had been moved by the plight of Darfur's people after visiting the region.

"I'm honoured to be taking over the fast for next three days," he said in a statement on his blog. "We cannot stand and watch as one million people suffer."

Farrow has been campaigning for years to raise funds for children in conflict zones, including Darfur, Democratic Republic of the Congo, Haiti, Chad and Nigeria.

In March, the Hague-based International Criminal Court issued a warrant for the arrest of the Sudanese president on charges of masterminding mass killings and deportations in Darfur.

Since then, he has expelled 13 foreign and three domestic humanitarian aid groups, accusing them of collaborating with the ICC.

Farrow is regaining her strength, eating oranges and drinking soup.

"While a million people in Darfur are facing starvation, I have the ability to end my fast," she said. "These people do not have that option."