Reports suggest as many as 140 people, including civilians, may have died in an attack on an airbase in Libya. It was originally thought 60 people died when a government-allied militia tried to take over the Brak al-Shati base on Thursday. The UN-backed government's defence minister and the commander of the militia have both been suspended pending an investigation. The prime minister's office has denied ordering the attack. A militia spokesman said they had "liberated the base and destroyed all the forces inside". The town's mayor said some aircraft had been set ablaze. Most of the dead were soldiers of the self-proclaimed Libyan National Army (LNA), an alliance in the east of the country which does not recognise the government in the capital, Tripoli. That force has been in control of the airbase since December. Its spokesman gave the new death toll of 140. "The soldiers were returning from a military parade. They weren't armed. Most of them were executed," he said. The UN's envoy to Libya, Martin Kobler, said he was "outraged" by reports of summary executions. Why is Libya so lawless? Profile: Libya's military strongman Khalifa Haftar of the LNA Guide to key Libyan militias The attack breached an informal truce between the rival forces that was reached earlier this month when the LNA's commander, General Khalifa Haftar, met the UN-backed Prime Minister Fayez al-Sarraj. The Tripoli government has set up an investigative committee to present its findings to the prime minister within 15 days.