The Mirage F1 was downed in Al-Hira region, 70 kilometres (50 miles) south of the capital, Haftar's self-styled Libyan National Army said on its Facebook page.

There was no immediate comment on the report from the Government of National Accord whose forces have been locked in battle with the Tripoli-based LNA since Haftar's fighters launched an offensive on April 4.

The LNA posted pictures of a man with an apparent head wound and blood-splattered uniform whom it identified as a "Portuguese mercenary".

In a video circulating on social media, the man is asked in English by an LNA fighter in the back of a pickup truck whether he was a soldier. "No, I am a civilian," he says.

The almost five-week-old battle on the southern outskirts of Tripoli has killed at least 432 people, wounded 2,069 and displaced some 55,000 others, according to the UN.

After initial advances for the LNA, its rivals have launched a counter-offensive, leading to a stalemate on the ground.

The two sides often accuse each of resorting to the use of foreign mercenaries and outside military assistance.

Libya has been mired in chaos since the ouster and killing of Moamer Kadhafi in 2011, with Haftar supporting a rival administration in the east of the country.

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