By Andrew Cawthorne

NAIROBI, Aug 31 (Reuters) - International aid agency Medecins Sans Frontieres (MSF) accused Ethiopia on Friday of denying it access to the remote Ogaden region where battles are raging between government troops and a rebel movement.

"The government of Ethiopia has denied MSF access to the five zones of the Somali region under military operation, often referred to as the Ogaden region," it said in a statement.

The government launched a campaign several months ago to flush out Ogaden National Liberation Front (ONLF) rebels after they carried out one of their bloodiest attacks to date, on a Chinese-run oil field, killing 74 people.

A United Nations fact-finding mission is in the region, assessing allegations by the rebels and rights groups of human rights abuses, as well as the food, water and health needs of Ogaden's ethnic Somali people.

"MSF urgently calls on the Ethiopian authorities to allow MSF teams to provide humanitarian assistance to vulnerable civilians living in that area," the group added in a statement released in Nairobi. But a senior Ethiopian official said the group's accusation was unfounded.

"Ethiopia does not have any no-go zone," Bereket Simon, special adviser to Prime Minister Meles Zenawi, told Reuters.

MSF said an "exploratory mission" by its personnel in the region prior to the ban had revealed "urgent health needs and a deteriorating humanitarian crisis."

"Despite a signed agreement with MSF, the authorities in Addis Ababa continue to deny MSF access to the area, in order to help the civilian victims of the conflict."

Earlier in August, the International Committee of the Red Cross (ICRC) said it had pulled out of the Ogaden following a government order.

The ONLF accuses Ethiopian authorities of blockading food relief, choking commercial trade and risking "man-made famine."

The government denies that, saying the ONLF are Eritrean-backed terrorists peddling lies to the world.

The claims and counter-claims are hard to verify, as the arid region, populated largely by nomadic herders, is effectively off-limits to most rights workers and journalists. (Additional reporting by Tsegaye Tadesse in Addis Ababa)

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