The United Nations’ acting Libya envoy said on Wednesday she was “quite optimistic” that ongoing talks between the warring sides would lead to a lasting ceasefire, after they agreed to reopen land and air routes across front lines.

Speaking midway through week-long talks, Stephanie Williams said the sides had also agreed to maintain “the current state of calm on the front lines and avoid any military escalation”.

“That is why I continue to be very optimistic that the parties here are going to reach a more lasting and permanent ceasefire,” she told a news conference at the U.N. in Geneva.

The first flights between Tripoli and the main eastern city Benghazi would resume this week, and the sides had agreed to make progress on an exchange of detainees, Williams said.

“With regard to the issue of the full resumption of oil production, the two sides agreed to delegate the commanders of the petroleum facilities guards from the east and west to work directly with a representative appointed by the National Oil Corporation to present a recommendation for the restructuring of the Petroleum Facilities Guards which will ensure the increase and continuation of the flow of oil,” Williams added.