Eastern Libyan forces attacked the sea port of Libya's capital on Tuesday as they targeted a Turkish vessel bringing in arms, an eastern official said according to a report by Reuters.
Eastern officials did not provide details about the alleged arms shipment at the port, which has remained open for food and other imports as rival factions battle for control of the capital.
The eastern-based Libya National Army (LNA) faction, led by Khalifa Haftar, started a campaign in April last year to take the city, which is seat of the internationally recognised government also backed by Turkey.
Authorities moved all ships including fuel tankers out of the port after Tuesday's attack, two port officials said. The Tripoli forces said the LNA had fired four missiles.
Since January, Turkey has sent several ships carrying arms and heavy trucks to Tripoli and Misrata, another western port, diplomats say.
The LNA, which is allied to a parallel government in the east, supported by the United Arab Emirates, Egypt, Jordan and Russian mercenaries. Eastern ports and airports are out of range of the Tripoli forces.
Tuesday's attack happened as officers from the Tripoli forces and LNA prepared to meet for a second round of talks in Geneva to establish a permanent truce.
Both sides refused again to sit in the same room, UN Libya envoy Ghassan Salame told reporters, although he said he was hopeful of making progress.
"So while the situation on the ground remains a situation where the truce is very fragile… nobody has so far reneged on the principle of accepting the truce and the political process is trying to find a way to move forward," he said.
He added that a ceasefire was not a precondition for advancing on other matters such as how to better distribute state revenues from oil, saying economic discussions were going "pretty well".
"It is going pretty well on the economic side, but it is harder on the military side," he said.
Salame said he had received conditions from tribesmen allied to eastern forces to lift a blockade of eastern oil export ports, but said they were quite general and would have to be tackled at a UN-led dialogue.
Tribesmen and other groups allied to the LNA joined with Haftar's forces a month ago to block major ports in eastern Libya and the southern Sharara oilfield, reducing oil output by more than 1 million barrels a day.
Salame had spoken to some tribal leaders to hear their conditions to end the blockade. A further round of discussions is planned in Geneva next week.