GENEVA, March 28 (Reuters) - Money from Europe and a charity co-founded by Hollywood actors George Clooney, Brad Pitt, Matt Damon and Don Cheadle will help maintain humanitarian flights in Darfur through April, the United Nations said on Friday.

The $6 million donated by Ireland, the European Union and the Clooney-backed Not On Our Watch will allow the U.N.'s World Food Programme (WFP) to hire helicopters and aircraft to ferry aid workers to Sudan's war-torn region for 30 days.

The WFP's air link carries some 8,000 aid workers from 160 organisations to, from and within Darfur each month, WFP spokeswoman Christiane Berthiaume said.

"We have received some funds which will allow us to maintain the flights for the month of April," she told a news briefing but added the reprieve is only short term as a further $71 million is needed to operate the service for the rest of 2008.

"It is vital to maintain the service especially at a time when insecurity reigns," she said.

The western Sudanese region of Darfur is the site of the world's largest aid operation. International experts estimate five years of conflict have killed 200,000 people and driven 2.5 million from their homes.

Aid workers are increasingly at risk in Darfur where rebel groups and militias have split into factions, some of them merely bandits without political agendas who prey on civilians for their own survival.

Bandits killed three WFP truck drivers in separate attacks earlier this month in Darfur and south Sudan.

Securing long-term funding for humanitarian flights in Sudan is essential, 14 international aid agencies said in a joint statement issued on Friday.

The agencies -- which include CARE Sudan, Catholic Relief Services and Oxfam International -- said that they rely on the WFP's air service to help them deliver aid to "many of the most inaccessible, insecure and poverty-stricken areas of Sudan".

In Darfur alone, the aid groups jointly assist more than 2 million people in areas currently only accessible by air, as roads are too insecure, according to the statement.

"A service upon which millions of people depend should not have to fear for its future every month," it said. (Reporting by Stephanie Nebehay, editing by Laura MacInnis and Mary Gabriel)

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