"We conducted an air raid targeting a field hospital south of Tripoli on Saturday, used as cover by terrorists to avoid being targeted," said a spokesman for Haftar's self-styled Libyan National Army.

Haftar's forces launched an offensive in April to try to wrest Tripoli from forces backing the internationally-recognised Government of National Accord.

Pro-GNA armed groups have weathered the initial onslaught and fighting has since remained deadlocked on the southern outskirts of the city, with both sides resorting to air strikes.

The GNA said the air strike on the field hospital south of Tripoli was carried out by "a Haftar warplane".

"It was a direct hit against the hospital which was packed with medical teams," health ministry spokesman Lamine al-Hashemi said.

But Haftar's spokesman Ahmad al-Mesmari said those killed were "not doctors but medical students", some of them linked to the Muslim Brotherhood.

"Some were imprisoned in the past for terrorism," he told a press conference.

Haftar, who controls much of eastern and southern Libya, has presented himself as a bulwark against Islamists.

He has received backing from Egypt and the United Arab Emirates, both of which are staunch opponents of the Muslim Brotherhood.

The UN humanitarian coordinator in Libya on Monday condemned the hospital attack, which she called a "disgraceful shelling... depriving thousands of people from accessing basic services".

Berangere Boell-Yousfi said that since the start of Haftar's offensive, 37 attacks had been registered on health personnel and facilities, killing 11 people and wounding 33.

The fighting since April has left nearly 1,100 people dead and wounded more than 5,750, according to the World Health Organisation.

More than 100,000 civilians have fled their homes.