ADDIS ABABA - The United Nations plans to send a fact-finding mission to Ethiopia's Ogaden region where separatist rebels who killed 74 people in an April attack say they are facing the toughest government crackdown in years.

The mission to assess allegations made by the rebels and rights groups of human rights abuses as well as the food, water and health needs of Ogaden's ethnic Somalis is expected to start on Aug. 30.

"It is my hope that the findings of this assessment mission will construct a clearer picture of the humanitarian situation in the region," U.N. Resident and Humanitarian Coordinator Fidele Sarassoro said in a statement on Wednesday.

"Equally important to us is that the findings of this mission also support the delivery of assistance to the people of the Somali region."

The remote region bordering Somalia has come under growing scrutiny since the government began a campaign two months ago to flush out Ogaden National Liberation Front (ONLF) rebels after they carried out one of their bloodiest attacks on a Chinese-run oil exploration field in April.

Rights groups accuse the military of burning homes, seizing livestock and shooting civilians in its hunt for the ONLF, which wants more autonomy for the area, which is believed to be rich in oil and gas.

The ONLF says a trade blockade is choking food supplies and causing starvation in the region inhabited mostly by nomadic herders estimated to number between four to 10 million.

Prime Minister Meles Zenawi calls the ONLF terrorists and says they are funded by neighbour and arch-foe Eritrea. He has repeatedly asserted his right to ensure security throughout the vast Horn of Africa country of 81 million.

The ONLF welcomed the mission saying it was a first step to addressing the "manmade humanitarian catastrophe" in Ogaden.

"We call on the United Nations not to limit the scope of this mission to a humanitarian assessment but to include a preliminary investigation of war crimes being committed against our people by the current ... regime," it said in a statement.

The mission will include staff from the office of the U.N. High Commissioner for Human Rights and the agencies dealing with child welfare, food and health.