The U.N. humanitarian chief has released $15 million in emergency aid to provide life-saving assistance to more than 85,000 people forced to flee recent fighting and military operations in the Iraqi city of Fallujah.

Stephen O'Brien said Monday that "people escaping Fallujah are in desperate need of assistance" and need urgent help "before this situation becomes a humanitarian catastrophe."

He said $15 million is a small portion of the $65 million needed to respond to Fallujah's needs, and he called on donors to urgently provide additional funds.

A U.N. appeal for $861 million for Iraq this year is only 36 percent funded.

Fallujah was the first Iraqi city to fall to Islamic State extremists in January 2014. Many IS militants have been routed but Iraqi forces were still battling remnants on Monday.