The majority of those killed in the attack on Monday in Wadi Rabea, 21 kilometres (13 miles) from the centre of the capital, Tripoli, were apparently migrants, while two were Libyan, the UN Libya envoy Ghassan Salame told the UN Security Council.
Photos posted by authorities showed several wounded people in bloodstained civilian clothes lying on beds in ambulances or medical facilities.
Malek Merset, a spokesman with the Tripoli-based health ministry, said at least 33 workers, mostly from Niger and Bangladesh, were taken to hospital for urgent treatment. Merset said seven people have died in the attack.
Libya has been split between rival camps based in Tripoli and the east since 2014, a result of the divisions that surfaced following the NATO-backed overthrow of longtime ruler Muammar Gaddafi three years earlier.
Tripoli has been under attack since April from forces loyal to renegade military commander Khalifa Haftar.
The offensive by his Libyan National Army (LNA) quickly stalled, and both sides have used drones and fighter jets to carry out air raids amid sporadic fighting.
The UN-recognised Tripoli-based Government of National Accord (GNA) blamed Monday’s attack on the LNA, which later issued a statement on combat operations that did not comment on the air raid.
LNA air attacks have often hit civilian areas in Tripoli, however, officials in eastern Libya contacted by Reuters News Agency on Monday said they had no information about an air attack by their forces.
“Regardless of whether the attack deliberately targeted the factory or was an indiscriminate attack, it may constitute a war crime,” the UN’s Salame said.
He also accused the LNA of causing civilian casualties by increased air attacks with unguided bombs, according to a transcript of his speech released by the UN mission in Libya.
The LNA has conducted more than 800 drone attacks, Salame said, while forces allied to the Tripoli government had carried out about 240.
Salame added that there had been intensified artillery fire directed at some Tripoli districts, although he did not name the LNA. He blamed a recent rise in violence on the growing use of mercenaries and private military contractors.
He did not identify these forces, but diplomats and Tripoli officials have said that hundreds of Russian mercenaries have been fighting on Haftar’s side since September.
More than 200 civilians have been killed and 128,000 displaced in the conflict, Salame said.
Last week, the United States called on the LNA to halt its offensive in Tripoli, warning against Russian interference.
Salame said Germany‘s attempts to hold a conference to bring an end to the conflict in Libya were continuing with another preparatory meeting planned for Wednesday.
He did not give a date for the main event.