GENEVA, Aug 4 (Reuters) - Tens of thousands of people have fled an assault by Islamic State on the town of Sinjar in northern Iraq on Sunday and are now surrounded, the United Nations said on Monday.
Islamic State inflicted a severe defeat on Iraq's Kurds on Sunday, when it made a rapid advance through three towns to reach the Mosul Dam, the largest in Iraq and a major source of electricity.
Previously, an estimated 308,000 people lived in the district of Sinjar. As the insurgents advanced, many fled to Sinjar mountain, or Jebel Sinjar, the U.N. Office for the Coordination of Humanitarian Affairs (OCHA) said in a statement.
"The exact number of displaced people on Jebel Sinjar is unknown; however, reports indicate that some 35-50,000 people displaced in nine locations, reportedly surrounded by ISIS (Islamic State) armed elements. There are reports, to be verified, of children already dying for lack of water and other assistance among those trapped," the OCHA statement said.
A further 30,000 people, mainly women and children, have made their way to Dahuk governorate in Kurdistan, with more expected in coming days, OCHA said.
"It is likely that displaced people on Jebel Sinjar are surrounded by ISIS forces. Based on a number of reports from the displaced population, there is an immediate need for water, food, fuel, shelter and health services."
The Iraqi army was assessing the possibility of humanitarian air drops over the mountain, the statement said.
Iraq's Prime Minister Nuri al-Maliki ordered his air force for the first time to back Kurdish forces against Islamic State fighters after the militants made their dramatic push through the north, state television reported on Monday.
The insurgents control the two roads down the Sinjar mountain and are attacking families moving along the roads, which lead to Sinjar town and the Syrian border crossing at Rabya, OCHA said.
It added that it had not independently verified the information but that it was "assessed as fairly reliable and probably true".
The Rabya border crossing itself was contested on Monday, with armed clashes between ISIS insurgents and Kurdish peshmerga fighters, OCHA said. (Reporting by Tom Miles; Editing by Larry King)