State news agency LANA said 15 people were lightly wounded as the raid hit a munitions depot in the town of Gharyan, 120 kilometres southwest of the capital.
The militias in Gharyan form part of Fajr Libya (Libya Dawn), an alliance including Islamists that was targeted by unidentified warplanes near Tripoli airport last month.
Washington said at the time that the United Arab Emirates and Egypt were behind the raids, although Haftar's forces also claimed that attack.
Haftar launched an assault against Islamists in the eastern city of Benghazi on May 16.
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Fajr Libya rejects the legitimacy of the elected parliament because it allegedly supported the air raids against its fighters at Tripoli airport.
The government, in turn, has accused Sudan and Qatar of supplying weapons to its Islamist opponents.
Parliament and the internationally recognised government relocated in August to Tobruk 1,500 kilometres east of Tripoli, as Islamist and nationalist militias battled for control of the capital.