GENEVA/TRIPOLI (Reuters) - The sea port in Libya's capital Tripoli was attacked on Tuesday, United Nations Libya envoy Ghassan Salame said, the latest violence in a battle for control of the home to the country's internationally recognized government.

A Reuters reporter in Tripoli, which eastern-based forces have been trying to take in a near-year long offensive, could see heavy smoke billowing from the port area. A port source said a warehouse had been hit, but no ship.

Tripoli's sea port has remained open for food and other imports since the eastern-based Libya National Army (LNA) faction, led by Commander Khalifa Haftar, started a campaign to take the city in April last year.

Salame spoke as officers from the Tripoli forces and LNA met for a second round of talks in Geneva to establish a permanent truce. Both sides again refused to sit in the same room, he told reporters.

"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 told reporters.

He also 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 U.N.-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.