GENEVA, July 31 (Reuters) - Young children among tens of thousands of refugees who fled civil war in the Central African Republic are suffering "alarming" malnutrition and need immediate aid, Medecins Sans Frontieres (MSF) said on Tuesday.

The Geneva-based international aid agency said "insufficient protection and assistance" for more than 26,000 refugees in 59 sites along Cameroon's eastern border "has led to a serious deterioration in their medical and nutritional situation."

MSF said in the town of Gbiti, in eastern Cameroon, about 4 percent of Central African Republic refugee children between 6 months and 5 years of age had severe acute malnutrition.

Some 23.8 percent -- or nearly one in four -- of children aged 5- to 10-years old had severe to moderate malnutrition.

At three sites -- Gbiti, Ngaoui and Ndokayo -- MSF said mortality rates were three to seven times above the emergency threshold.

"Given that young children are most vulnerable to malnutrition, these figures simply reflect the worsening food situation of those populations and the delay in sending assistance," it said in a statement.

MSF said it had begun distributing food rations in the region "as an interim measure until the United Nations starts coordinating the general distribution of food".

The food rations are accompanied by active screening and the implementation of a medical and nutritional care strategy for the most urgent cases, it added.

The United Nations said last month attacks by rebels along Cameroon's border with the Central African Republic were hampering efforts to aid those who fled violence in the region.

Jacques Franquin, a representative for the U.N. refugee agency UNHCR in Cameroon, told Reuters at the time "an almost permanent situation of insecurity" near the border, including kidnappings, made it impossible to deploy personnel there.

The Central African Republic has suffered decades of instability and military coups since it won independence from France in 1960.

Humanitarian agencies estimate about 290,000 Central Africans have been forcibly displaced in the past 18 months, including 78,000 who have crossed into neighbouring Cameroon, Chad and Sudan.

The International Committee of the Red Cross has said those displaced by the fighting were living in "extremely poor conditions" and without basic medical care.

The ICRC is one of few aid agencies still operating in the northwest of the country, where the U.N. suspended its operations after a French aid worker was shot dead in June.

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