The self-styled Libyan National Army told The Independent its forces took down a Mirage F1 French attack aircraft over a suburb of the capital.
The LNA is currently battling armed groups and militias affiliated with the United Nations-recognised government in Tripoli.
A LNA spokesperson, who asked to remain unnamed, said the pilot, a Portuguese national, survived and was now in its custody.
They also sent photos of the alleged crash site and the pilot, which cannot be independently verified.
The photos sent by the spokesperson appeared to show a foreign national, whose head, face and clothes were covered in blood, sitting on a chair in an office flanked by LNA officials.
The terrified looking pilot, who has two tattoos on his chest and arm, appears to be wearing a military pilot jump suit.
In one image, LNA commander Major General Abdulsalam al-Hassi, who is head of Haftar’s operations room in the area, is photographed standing behind him.
A man in military fatigues can be seen attending to a wound on his head.
“We downed a Mirage F1 and this is the pilot from Portugal,” a spokesperson for the forces told The Independent.
“He is safe… [and has has been] treated from wounds due to his crash,” the spokesperson added.
Earlier, a fake Facebook account falsely attributed a spokesperson from the LNA saying the jet was a European surveillance plane used by the EU’s Operation Sophia in monitoring illegal migrant smuggling routes in the Mediterranean.
The LNA issued a statement denying reports that the pilot was working for the EU and that he was being returned to his country.
This is not the first report of the use of mercenaries in Libya.
Both sides have traded accusations of foreign support, which may contravene a UN arms embargo on the country since 2011.
Haftar’s forces have repeatedly claimed militias fighting on behalf of the UN-recognised Government of National Accord have used multiple foreign mercenaries including pilots and soldiers from the US, Portugal, Ecuador, Turkey and the Ukraine.
Fayez al-Serraj, the head of the GNA, meanwhile has accused Haftar of being backed by foreign powers but declined to identify which countries.
In the past Haftar has allegedly received weapons support from Egypt, the UAE and Russia.
Haftar surprised the UN-backed authorities by launching a military operation on Tripoli just weeks before a scheduled 14 April meeting with Sarraj, during which they were supposed to hammer out details of plans to host elections later in the year.
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