The shipments were described as “spare parts”, including mirrors, lights, indicators, brake systems and tyres, dispatched under the authority of the Libyan embassy in Ankara, bound for the Ministry of Interior in Libya.

“NO DG,” or dangerous goods, said one 27 May air waybill. “NO WEAPONS, NO AMMO.”

But the flights immediately raised suspicions. As the 10 or so Ukraine Air Alliance flights exited Turkish air space from Istanbul to the Libyan city of Misrata in late May and June this year, they turned off the transponders, making them invisible to commercial tracking websites.

What they were hiding, United Nations investigators say, was nearly 54 tonnes of parts to assemble sophisticated Bayraktar military drones to be used on Libyan battlefields, in violation of an international arms embargo.

The plane shipments are detailed in a new report by a UN panel of experts assembled to report on the conflict in the North African nation.

The hefty 376-page report alleges that the United Arab Emirates, Jordan and Turkey, all Western military partners or allies, are repeatedly using subterfuge to get weapons into Libya but sometimes “blatantly” flouting an international arms embargo prohibiting arms to Libya.

Libya airstrike: Migrant detention centre hit in airstrike, killing 60 Show all 9 1 /9 Libya airstrike: Migrant detention centre hit in airstrike, killing 60 Libya airstrike: Migrant detention centre hit in airstrike, killing 60 Migrants carry the remains of their belongings from among rubble at a detention centre for African migrants that was hit by an airstrike in the Tajoura suburb of Libyan capital Tripoli on July 2 Reuters Libya airstrike: Migrant detention centre hit in airstrike, killing 60 Security and emergency responders work at the site of an airstrike that hit a detention centre for African migrants near Tripoli, Libya on June 2 Reuters Libya airstrike: Migrant detention centre hit in airstrike, killing 60 Security and emergency responders work at the site of an airstrike that hit a detention centre for African migrants near Tripoli, Libya on June 2 Reuters Libya airstrike: Migrant detention centre hit in airstrike, killing 60 The point of impact of a bomb that was dropped on a detention centre for African migrants near Tripoli, Libya on June 2 AFP/Getty Libya airstrike: Migrant detention centre hit in airstrike, killing 60 Blood stains are seen among debris following an airstrike that hit a detention centre for African migrants near Tripoli, Libya on June 2 Reuters Libya airstrike: Migrant detention centre hit in airstrike, killing 60 A woman picks up clothes among rubble at a detention centre for African migrants that was hit by an airstrike in the Tajoura suburb of Libyan capital Tripoli on July 2 Reuters Libya airstrike: Migrant detention centre hit in airstrike, killing 60 Migrants gather outside following an airstrike on the detention centre in the Tajoura suburb of Libyan capital Tripoli on July 2 AFP/Getty Libya airstrike: Migrant detention centre hit in airstrike, killing 60 A man carries his belongings from among rubble at a detention centre for African migrants that was hit by an airstrike in the Tajoura suburb of Libyan capital Tripoli on July 2 Reuters Libya airstrike: Migrant detention centre hit in airstrike, killing 60 Migrants sit together with their remaining belongings in the yard of the detention centre that was hit by an airstrike in the Libyan capital of Tripoli on July 2 Reuters

On Tuesday, Turkish President Recep Tayyip Erdogan said a new military deal signed with al-Serraj’s government did not include troop movement, but that it could, if requested. He insisted that would not violate the arms embargo.

Both sides in Libya’s ongoing civil war have also employed foreign mercenaries, according to the report, which was submitted to the Security Council this week.

The latest stage in Libya’s armed conflict began in April, when forces under the command of Libyan warlord Khalifa Haftar launched an attack on Tripoli in an attempt to quickly wrest control of it from the UN-backed Government of National Accord led by Fayez al-Serraj.

But western Libyan forces quickly united and regrouped, fending off the offensive and gaining back some ground.

Eight months later, the war drags on, locked in a stalemate on the outskirts of Tripoli that endangers Libyan civilians as well as migrants stuck in the country’s most dense urban areas.

“Neither side has the military capability to effectively decide the outcome to their advantage,” says the report, which covers much of the last year.

Meanwhile the conflict has given once largely subdued Isis networks a chance to regroup. In July, Isis’s local leader, Abu Musab al-Libi, declared Libya one of its main theatres, and the report says the group is financing itself by robbery, smuggling, extortion, kidnap for ransom and taxing human trafficking networks.

The report identifies numerous international weapons shipments to the two belligerents, and describes in detail how and when Mr Haftar’s Libyan National Army largely declined to participate in the research, asserting only in October that it had appointed a panel of three officers to respond to a dozen communications sent by the UN panel over the previous year.

Despite the internationalisation of the conflict, many of the countries directly or indirectly involved in the Libya war are refusing to provide information to the UN investigators. The United States failed to reply to all seven communications sent by the panel, while Russia, Turkey, Jordan and the United Arab Emirates also failed to reply to most inquiries.

The panel of experts identifies multiple weapons shipments from Jordan, the UAE and Turkey in violation of UN Security Council resolution 1970, passed in 2011.

Among the weapons obtained by Mr Haftar is a Pantsir S-1 surface-to-air missile system spotted repeatedly throughout Libya while mounted on a particular truck.

“Only the United Arab Emirates uses this configuration for its Pantsir S-1 systems, which was supplied to them after 2011,” says the report. “The complexity and costs of the system make it very unlikely that the United Arab Emirates has supplied it to any other entity who could have subsequently transferred it to Libya.”

Migrants gather in aftermath of airstrike in Tripoli, Libya

The panel notes that numerous of Mr Haftar’s officers received Special Operations training in Jordan, in violation of UN rules.

The report identified five Sudanese armed militias and four Chadian groups providing ground forces to both sides, with Mr Haftar’s fighters receiving the bulk of the foreign support.

Both sides in the conflict have also apparently hired foreign pilots and used combat drones to conduct airstrikes, some with precision-guided munitions.

The report notes that operating such weaponry is complex and “beyond the current known capability of the military units” on either side, suggesting foreign involvement.

In June, a US former Air Force pilot was released from LNA captivity after his fighter jet was apparently shot down by Haftar’s forces.

The report also chronicles the damaging effect the war is having on Libyan banking institutions and oil infrastructure, and describes various human rights abuses by both sides in the conflict.