By Megan Davies

UNITED NATIONS, Aug 1 (Reuters) - The aid group Doctors Without Borders said on Friday it has pulled staff out of two locations in Sudan's war-torn Darfur region, which the United Nations said will leave 65,000 people without medical aid.

The group said in a statement it had been forced to evacuate its staff from the Tawila and Shangil Tobaya areas of North Darfur after a series of violent attacks against them.

The organization said that over the past week, groups of armed men had entered the Doctors Without Borders compounds at night, held staff at gun point and stolen money and valuables.

The top U.N. humanitarian official called on Khartoum to take action to protect humanitarian aid workers in Darfur, where the deteriorating security situation has forced aid agencies to reduce rations for hordes of hungry people there.

"The Sudanese government have a responsibility to ensure security throughout their territory," John Holmes, under-secretary-general for humanitarian affairs, said in a statement. He said this year, 180 humanitarian vehicles have been hijacked, 145 aid workers kidnapped and nine killed.

"Impunity for such attacks must end," he said. "Hundreds of thousands of people rely on the assistance these aid organizations deliver and we cannot afford to have them absent from Darfur."

Some 17,000 aid workers are deployed in Sudan's arid western region, where international experts estimate at least 200,000 people have died and 2.5 million been driven by their homes since mostly non-Arab rebels took up arms in 2003.

A year ago, the U.N. Security Council authorized a combined force between the U.N. and African Union to deploy 26,000 troops and police for Darfur, but the mission is struggling with only 9,500 in place.

The U.N. Security Council renewed the mandate for peacekeepers in Darfur on Thursday for another year.

The resolution, however, was criticized by Washington for raising concerns about moves by the International Criminal Court's chief prosecutor to indict Sudanese President Omar Hassan al-Bashir for war crimes and genocide in Darfur. (Editing by Eric Walsh)

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