The United Nations says fighting between the self-styled Libyan National Army and militants has killed at least 17 civilians, including two children, in Libya's eastern city of Derna.

The U.N. Support Mission in Libya said in a statement Friday that the fighting has injured 22 others, including seven children, since May 16.

It said an explosion on Wednesday killed seven people and wounded seven others as they were attempting to leave Derna. It added that dozens of families have left the city.

The LNA, led by Field Marshal Khalifa Hifter, has surrounded the city of 150,000 people for years. Clashes have been ongoing since April.

Hifter announced his intention to "liberate" Derna in May.

Libya descended into chaos following the 2011 uprising that toppled ruler Moammar Gadhafi.