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 spokesperson said on Friday, amid fierce fighting since late April.The LNA forces have captured "more than 75% of Derna and forced out terrorists from most of the city," Ahmed al-Mesmari told The Associated Press.'"Our forces already control the seaport of the city and much of its eastern coast," he said. "Just a few pockets remain under control of extremist groups and the armed forces have been clearing them," he said.He added that the forces have been advancing on the city from all sides. The LNA released a video footage on Wednesday showing fierce battles raging, apparently inside a neighborhood in Derna.Field Marshal Khalifa Haftar, 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.Haftar's forces have surrounded the city of 150 000 people for years. Haftar said on 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. Spokesperson 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 UN Support Mission in Libya said last week that fighting has 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 and later killed long-time ruler Moammar Gaddafi. The country is now split between rival governments in the east and west, each backed by an array of militias. Haftar is allied with the eastern-based administration that is at odds with the UN-backed government based in the capital, Tripoli. * Sign up to News24's top Africa news in your inbox: SUBSCRIBE TO THE HELLO AFRICA NEWSLETTERFOLLOW News24 Africa on Twitter and Facebook.