The U.N. migration agency says recent clashes between rival Libyan militias for control of Tripoli have displaced more than 18,000 people.

U.N. spokesman Stephane Dujarric said on Monday in New York that the International Organization for Migration reported that 13 civilians are among the 146 killed so far in clashes since the self-styled Libyan National Army launched a major military offensive on April 5.

Dujarric says around 3,000 migrants remain trapped in detention centers in and close to conflict areas.

The fighting pits the Libyan National Army, led by commander Khalifa Hifter against militias affiliated with Tripoli's U.N.-backed government.

The clashes threaten to re-ignite civil war such as the 2011 one that toppled and killed longtime dictator Moammar Gadhafi. Libya is split between rival governments in the east and west.