Warplanes struck overnight at an airbase that was recently recaptured by Libya's internationally recognised government from eastern forces with help from Turkey, a military source with the eastern forces and a resident nearby said.
The strikes were carried out by "unknown aircraft", the military source with the Libyan National Army (LNA) of eastern-based commander Khalifa Haftar said.
A resident at the nearby town of Zintan said explosions were heard from the direction of the base.
Watiya's recapture in May by the Government of National Accord (GNA) in Tripoli marked the start of a sudden collapse of the LNA's 14-month assault to seize the capital and its retreat along the coast to the new frontlines.
Turkish support was vital to the GNA in turning back the LNA offensive with advanced air defences and drone strikes that targeted Khalifa's supply lines and troop build-ups.
A Turkish source said last month that Turkey was in talks with the GNA to establish two bases in Libya, one of them at Watiya, the most important airbase in western Libya.
Turkey's Defence Minister Hulusi Akar was in Tripoli for meetings with the GNA on Friday and Saturday and Akar swore to do all that was necessary to help it, a Turkish defence ministry statement said.
The LNA is backed by the United Arab Emirates, Russia and Egypt. During its advance towards Tripoli last year, the LNA was assisted by Egyptian and UAE airstrikes.
Last month, the United States said Russia had sent at least 14 MiG29 and Su-24 warplanes to an LNA base via Syria, where their Russian airforce markings were removed.
Turkish involvement in Libya has also angered France and Greece and French Foreign Minister Jean-Yves Le Drian has warned of new sanctions on Ankara.
The GNA and LNA are now mobilising forces at the new frontlines between the cities of Misrata and Sirte. Egypt has warned that any Turkish-backed effort to take Sirte, which the LNA captured in January, could lead its army to directly intervene.