An air war in Libya is intensifying as rival forces in the divided country try to break a military stalemate, heightening significantly the risk of civilian casualties.

At least 45 people were killed and dozens wounded in an airstrike last Sunday that targeted a town hall meeting in south-western Libya. The forces of Khalifa Haftar, the 75-year-old military strongman who controls much of the east of the country, have been blamed.

Witnesses said the attack on a residential district of Qalaa in the town of Murzuq came from a drone.

The death toll, which included many children, represents one of the largest single losses of civilian life since the civil war began in 2011 following the fall of the veteran dictator Muammar Gaddafi.

In June, more than 50 people were killed when an airstrike demolished much of a migrant detention centre on the outskirts of Tripoli. Haftar’s forces were also blamed for that attack.

The new strike comes almost exactly four months after the former general launched his self-styled Libyan National Army against Tripoli, the seat of the rival Government of National Accord (GNA).

Haftar’s offensive has so far led to more than a thousand civilian deaths and derailed diplomatic efforts to reconcile the two main armed political factions in Libya.

After rapid early gains, Haftar’s forces have stalled as resistance by a coalition of militias fighting for the GNA has hardened.

This has led to an increasing deployment of air power to gain tactical advantage in what has become a stalemate and to avoid further military casualties, experts say.

The shift has been fuelled by the provision of drones and other weapons systems by regional and international powers backing both factions.

“The air war will intensify, as long as international reaction is pretty non-existent. The conclusion is that [actors] can get away with this, and they can do it again, even in more densely populated areas. These are thresholds that keep getting crossed,” said Jalel Harchaoui, an expert at the Clingendael Institute in The Hague.

Haftar is supported by Egypt, the United Arab Emirates and Saudi Arabia, while the GNA, recognised by the UN as the legitimate government of Libya, is backed by Turkey and Qatar.

In June, Antonio Guterres, the UN secretary general, called for the UN arms embargo in place since 2011 to be respected.

Last week an airstrike by a drone destroyed a Ukrainian cargo plane at an airbase in Misrata, a coastal city controlled by the GNA.

Ukrainian authorities said the aircraft, arriving from Turkey, was carrying humanitarian aid. The LNA said it was carrying weapons for its enemies.

The strike came shortly after two cargo planes had been destroyed at Haftar’s main forward airbase in Jufra.

The attack on Murzuq on 4 August is thought by experts to have involved a Chinese-made armed drone probably flown from one of the airbases built by the UAE in Libya.

The Wing Loong drones were first deployed in the east of the country in 2016.

Arnaud Delalande, an expert in Libyan military aviation and its role in the conflict, said small fleets maintained by both sides had been depleted by enemy fire, accidents and mechanical failures in the course of recent fighting. Though the LNA already had drones deployed, operated by the UAE, the GNA obtained its unmanned aircraft from Turkey.

“Both sides needed other options and drones were the best choice,” Delalande said.

Some other airstrikes in recent weeks have been made by what appear to be more modern F-16 or Mirage fighters. Other precision strikes have taken place at night. This suggests the involvement of either Egypt or Emirati planes and pilots, analysts say.

The victims in Murzuq last Sunday were from the Tebu tribe, which has opposed the expansion of Haftar’s influence into south-western Libya and has fought with local Arab tribes allied with the LNA.

The target was a government building at which more than 200 local dignitaries were gathered to resolve local disputes.

Guests from a wedding which had been held in the building earlier in the day were also killed when they attempted to help casualties and were hit by a second strike, Dr Ahmed Adey, a doctor in the town who treated some of the injured people, told the Guardian.

Many casualties struggled to get treatment.

“There’s only one hospital with no resources in the town, and it’s dangerous for the Tebus to travel to get treatment because of their issues with the tribal militias that are supported by Haftar,” Ismail Bazinga, a medical student from Murzuq who has assisted in the care of casualties, told the Guardian on the phone.

There are reports of casualties from the bombing dying after being stopped at checkpoints manned by fighters from other communities as relatives tried to take them to coastal cities for medical help.

With its 50,000 inhabitants, mostly from the Tebu ethnic group, and its ancient fortress, the oasis town is located almost 900km (550 miles) by road south of Tripoli.

A spokesperson of the LNA said in a video on Facebook that the airstrikes had targeted militias from neighbouring Chad.

In a statement the United Nations Support Mission in Libya (UNSMIL) said it was extremely concerned by reports of violence in Murzuq, including the airstrikes.

“Indiscriminate attacks constitute a blatant violation of international humanitarian and human rights law and may amount to war crimes,” a statement said.

The EU said “indiscriminate attacks on densely populated residential areas” may amount to war crimes and called for those breaching international humanitarian law to be brought to justice.

