* Most cases in Darfur, a region already ravaged by war
* No effective treatment for yellow fever
* Half of targeted population vaccinated so far - WHO
KHARTOUM, Dec 3 (Reuters) - Yellow fever has killed 164 people over the last three months in Sudan's Darfur, the World Health Organization (WHO) said on Monday, an arid region the size of Spain where fighting and banditry makes access particularly difficult.
Healthcare is provided almost entirely by aid agencies in parts of Darfur, where rebels took up arms in 2003 complaining of neglect by the central government hundreds of miles away in Khartoum.
The latest outbreak of mosquito-borne yellow fever has been concentrated in central Darfur, the WHO and Sudan's health ministry said in a joint statement.
"Between 2 September and 29 November, the total number of suspected yellow fever cases has reached 677, including 164 deaths," the statement said.
Nearly half the yellow fever cases were in people between the ages of 15 and 30, it said, and about a quarter were children aged five to 15.
There is no effective treatment for the haemorrhagic fever, but there is a vaccine. The WHO said last month that some 3.6 million people would be vaccinated in affected areas of Darfur.
Monday's statement said more than half of the targeted population had been vaccinated by Nov. 30.
The United Nations and human rights groups estimate that hundreds of thousands of people have died in Darfur's conflict, The government has put the death toll at 10,000.
The International Criminal Court has issued an arrest warrant for Sudan's President Omar Hassan al-Bashir on charges of war crimes in the region. He denies the allegations. (Reporting by Alexander Dziadosz; Editing by Louise Ireland)