Air traffic control recordings obtained by the Middle East Eye suggest British, French, Italian and US forces have been coordinating air strikes in support of renegade Libyan general Khalifa Haftar.
The leaked tapes, which could indicate the countries are helping Haftar fight rebels in the east, appeared to confirm that a joint operations base exists - something which the London-based media organisation has previously reported.
"What's clear is that Western forces are helping Haftar coordinate air strikes in eastern Libya, which is where his base of control is. But the targets there aren't actually Islamic State of Iraq and the Levant (ISIL, also known as ISIS)," Karim el Bar, the journalist who reported the story, told Al Jazeera.
"They [the targets] are his [Haftar's] political enemies - some of whom are Islamists, some of whom have other political affiliations ... he's undermining the government in Tripoli."
Conversations between Libyan pilots and the air traffic controllers at Benina airbase, one of Haftar's vital military facilities, can be heard in the leaked audio, in both Arabic and English. French, Italian, American and British accents are audible.
Haftar helped former Libyan leader Muammar Gaddafi seize power in 1969 and was once a key figure in the army before being exiled to the US in the late 1980s. He spent the next several decades plotting to oust Gaddafi.
Last year, Haftar launched a self-declared campaign to drive armed groups from Libya's second biggest city, Benghazi. He has refused to support a UN-backed unity government, based in the capital Tripoli, because his forces were once loyal to a rival government.
"The government in Tripoli is launching an offensive in Sirte against ISIL, and so we have this bizarre situation where Western governments are diplomatically and publicly supporting the government in Tripoli, but then their militaries are supporting Haftar in the east," el Bar said.
The leak could cause diplomatic headaches for the countries implicated, in light of Haftar's refusal to support the unity government.
Forces loyal to the general have also been accused of fighting groups taking part in the Western-backed campaign against ISIL.
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"Benghazi, good morning, Ascot 9908," says a man with a British accent, in one of the recordings. "Ascot 9908, just letting you know we are in contact with Benghazi airfield."
French and Italian operators appear to be directing air traffic in most recordings.
Pilots with American accents also feature, using the call signals "Bronco 71" and "Mustang 99" - both are names of American cars.
After participating in the Libyan revolution in 2011 and Gaddafi's overthrow, Haftar faded into the background until February 2014, when he called on Libyans to rise up against the General National Congress (GNC) - the newly elected parliament.
Then, at the time of his dramatic televised address, groups such as the al-Qaeda affiliate Ansar al-Sharia had taken over Libya's second city of Benghazi and its surrounding towns and villages, fighting a war against military, police and public officials.
In May 2014, he launched Operation Dignity to combat what he called hard-line militias in and around the city. In March 2015, Libya's newly elected House of Representatives, which replaced the GNC, appointed him the commander of the Libyan National Army.
In the past two years, forces loyal to Haftar have pushed armed groups out of Benghazi to as far as Derna, 250km to the city's east.
READ MORE: The conflict explained
But his potential role in any future national military has been one of the biggest roadblocks in attempts to achieve Libyan unity.
He is reportedly unhappy with the line-up of the UN-brokered Government of National Accord because responsibility for security has been given to another officer, Ibrahim al-Barghathi.
Several reports since the beginning of Operation Beginning suggest that Haftar receives considerable support from foreign backers, the UAE and Egypt in particular.
Some analysts say that his foreign backing has made him less willing to compromise on a unity government.
Now, as the UN-backed government attempts to route ISIL out of its stronghold in Sirte, Haftar has been accused of pursuing a separate war against a group that helped push ISIL out of Derna last year.
The Shura Council of Mujahideen in Derna - an anti-ISIL Islamist coalition - was key in last year's fight in the port city. The UN Support Mission in Libya condemned Haftar's air strikes there and warned that the resulting civilian casualties could constitute a war crime.
"Basically he doesn’t want to have any rivals in the east and he considers everyone, even loosely associated with political Islam, as terrorists," Libya specialist Mattia Toaldo, a senior policy fellow with the European Council on Foreign Relations, told Middle East Eye. "Much like his Egyptian patrons."
The Middle East Eye's el Bar told Al Jazeera: "You have to wonder why Western governments are supporting him if he's not going directly after ISIL. If you're going to have political reconciliation in the country, you're going to have to bring these groups [that Haftar is targeting] in."
Source: Al Jazeera