CAIRO (AP) — The self-styled Libyan National Army seized most of the eastern coastal city of Derna from extremist groups who have controlled it for years, a spokesman said Friday, amid fierce fighting since late April.

The LNA forces have captured "more than 75 percent of Derna and forced out terrorists from most of the city," Ahmed al-Mesmari told The Associated Press.

A "few pockets remain under control of extremist groups and the armed forces have been clearing such pockets," he said.

Field Marshal Khalifa Hifter, who leads the LNA, announced in May that his forces launched a military operation aimed at "liberating" Derna from extremist groups, led by the Derna Protection Forces, an alliance of Islamists and anti-Haftar fighters.

Hifter's forces have surrounded the city of 150,000 people for years. Hifter said Monday that "the hour of victory is approaching, as is the announcement that the city of Derna is free of terrorism."

The United Nations human rights office voiced concerns on Friday over the escalating risks to the population in Derna. Spokeswoman Elizabeth Throssell said the city's only hospital has been closed since June 5 and they have documented the deaths of three women as a result of the lack of oxygen supplies.

"There have been increasing allegations that civilians have been arbitrarily detained, while others have been prevented from leaving the city," she said.

The U.N. Support Mission in Libya said last week fighting killed at least 17 civilians, including two children, and wounded 22 others in Derna since May 16. UNSMIL said dozens of families were forced to leave the city.

It urged the warring parties to ensure "unimpeded humanitarian access and facilitate the safe exit of civilians wishing to leave the city."

Libya descended into chaos following the 2011 uprising that toppled ruler Moammar Gadhafi. The country is now split between rival governments in the east and west, each backed by an array of militias. Hifter is allied with the eastern-based administration that is at odds with the U.N.-backed government based in the capital, Tripoli.