Five doctors were killed in an air strike by forces of Libyan strongman Khalifa Haftar on a field hospital near the capital, the health ministry of the UN-recognized government said.
Haftar's self-styled Libyan National Army launched an offensive in April to try to wrest Tripoli from forces of the Government of National Accord which is based in the capital.
Pro-GNA forces have weathered the initial onslaught and since then fighting has remained deadlocked on the outskirts of the city, with both sides resorting to air strikes.
"The field hospital located on the airport road (south of Tripoli) was hit by an air raid. Five doctors were killed and seven other people, including rescuers, wounded," health ministry spokesman Lamine al-Hashemi told AFP.
The strike occurred on Saturday and was carried out by "a Haftar warplane", he said.
"It was a direct hit against the hospital which was packed with medical teams," Hashemi added.
Mustafa al-Majai, the spokesman for the GNA's Burkan al-Ghadab (Volcano of Rage) military operation, said it was the third time that the hospital was targeted in an air strike.
There was no immediate confirmation or denial of responsibility from Haftar's forces.
On July 16, three doctors and a paramedic were wounded in a strike on the Swani hospital near the capital, the second time it was targeted.
The World Health Organization (WHO) and rights groups have repeatedly called on both sides in the conflict to spare medical personnel, clinics and hospitals.
The fighting since April has left nearly 1,100 people dead and wounded more than 5,750, according to the WHO. More than 100,000 civilians have fled their homes.
Haftar's forces also hit a school near Tripoli on Saturday, causing material damage. No students were in the school as the strike coincided with a holiday.
The battle between rival militias for control of the Libyan capital raged amid increased fighting over the past the past 24 hours, officials said Saturday, with both sides relying heavily on airpower to make progress.
Libyan officials, who spoke on condition of anonymity because they were not authorized to brief reporters, said Haftar's LNA launched airstrikes overnight against an air base in the western city of Misrata.
The officials said the LNA also took control of the al-Naqliyah military camp in the south of Tripoli.
They said Haftar forces were also fighting to cut off a major route linking Misrata to Tripoli, which, if they succeeded, would be a major blow to the U.N.-supported government.
In past weeks, the battle lines have changed little, with both sides dug in and shelling one another in the southern reaches of the capital.
The LNA is the largest and best organized of the country's many militias, and enjoys the support of Egypt, the United Arab Emirates (UAE) and Russia. But it has faced stiff resistance from fighters aligned with the U.N.-recognized government, which is aided by Turkey and Qatar.
After their initial attack on Tripoli was halted, the LNA forces lost control of the strategic city og Gharyan to GNA forces in late June.
The Libyan officials said the LNA airstrikes on the Air Force Academy in Misrata came after armed groups allied with Tripoli launched an air attack a day earlier against al-Jufra air base, the LNA's main forward airfield in the Tripoli offensive.
The officials also said heavy fighting was underway in Abu Salim district, about 7 kilometers (4 miles) from Tripoli's center, and in Salah al-Deen, an area that saw previous clashes between rival militias in September.
The LNA's media office said in a statement that over 10 airstrikes had targeted a control room for Turkish-made drones, along with other targets in Misrata and the western coastal city of Sirte.
A spokesman for the Tripoli-based militias confirmed they had launched an air attack Friday against al-Jufra air base.
The LNA released a statement saying its forces had taken control of the al-Naqliyah military camp and advanced in different parts of southern Tripoli.
Fighting for the capital has emptied entire neighborhoods of civilians. Thousands of African migrants captured by Libyan forces supported by the European Union are trapped in detention centers near the front lines. On July 3, at least 44 people were killed and more than 130 were wounded when Haftar's forces hit a migrant detention camp near Tripoli in an air strike.
On Saturday, Libya's coast guard said it had intercepted 89 Europe-bound migrants in a rubber boat the previous day. The coast guard is continuing its search for the bodies of up to 150 people, including women and children, whose boats capsized Thursday in the Mediterranean Sea while attempting to cross to Europe.
Libya slid into chaos after the 2011 uprising that toppled and killed long-ruling dictator Moammar Gadhafi. Armed groups have proliferated, and the country has emerged as a major transit point for migrants fleeing war and poverty for a better life in Europe.