KHARTOUM (Reuters) - Fighting over a gold mine in Sudan's Darfur region has forced 100,000 people to flee and brought the closure of all public offices and schools in one town to accommodate the displaced, the United Nations said on Thursday.

Conflict has raged in the vast arid region of Darfur for almost a decade since mainly non-Arab tribes took up arms against the Arab government in Khartoum in 2003, accusing it of political and economic neglect.

Violence has ebbed since a peak in 2003/2004 but has picked up again in the past few months.

This month heavy fighting broke out between two Arab tribes over gold in the Jebel Amer area in North Darfur, displacing or severely affecting 100,000 people, the United Nations said. It had previously reported 70,000 displaced people.

"Many of these people are living in the open in appalling conditions," the United Nations Office for the Coordination of Humanitarian Affairs (OCHA) said in a report.

Some 65,000 people had fled to the town of El Sireaf, the United Nations said, adding that all public offices and schools had been closed in the area to shelter displaced people.

The United Nations said it had delivered more than 600 tonnes of food but had been unable to assess the scale of conflict because the authorities had not allowed a U.N. delegation to travel to the affected area.

Some 30,000 people were displaced by separate fighting between the army and a rebel group in the central Jebel Marra area, the United Nations said two weeks ago.

Events in Darfur are hard to verify as Sudan restricts travel by journalists, aid workers and diplomats. This week security agents denied Reuters a travel permit to attend a government-sponsored disarmament conference in West Darfur, despite an official invitation. No reason was given.

Rebel divisions and a string of broken ceasefires have scuppered years of international mediation and several rounds of peace talks. Banditry has also spread.

The International Criminal Court has issued arrest warrants for Sudan's President Omar Hassan al-Bashir and other Sudanese officials to face charges of masterminding war crimes in Darfur. They deny the charges and refuse to recognize the court.

Human rights groups and the United Nations estimate hundreds of thousands of people have died in Darfur's conflict. The government says around 10,000 people have been killed.

(Reporting by Ulf Laessing; Editing by Stephen Powell)