The United Nations special envoy for Libya Martin Kobler met eastern political 'rebel' Ali al-Qatrani in Cairo, Kobler tweeted on Wednesday.
"Long and Open meeting with Ali al-Qatrani in Cairo. Only dialogue is the way to peace in a united Libya," Kobler wrote on Twitter.
"Really appreciate his frankness, openness and clarity," read a second tweet from Kobler.
Qatrani, who hails from Libya's eastern coastal region of Cyrenaica, is one of two people appointed to the UN-backed Libyan national unity government's Presidential Council who have boycotted the body since it arrived in Tripoli in March.
The Presidential Council has the role of head of state of Libya and temporary command of the Libya's army under a UN-backed accord signed in December by the country's rival political factions to create the national unity government and end a five-year civil war.
Qatrani, like the internationally recognised parliament in the eastern city of Tobruk's speaker, Aguila Saleh, is a supporter of army chief Khalifa Haftar, who has refused to recognise the national unity government.
Haftar, who observers say could decide chaos-wracked Libya's future, last week refused to attend a meeting Kobler.
The internationally recognised government in Tobruk has refused to hand over power to Libya's national unity government until it receives a vote of confidence from the Tobruk parliament.
Tobruk has criticised visits by foreign diplomats to Tripoli for meetings with the national unity government's prime minister-designate Faiz al-Sarraj as "contrary to diplomatic norms and ethics".
Libya plunged into chaos after a NATO-backed revolt that overthrew dictator long-time Muammar Gaddafi in 2011. An Islamist-backed administration in Tripoli has been vying for power with the Tobruk government, each of which is backed by a multitude of militias.
The Islamic State jihadist group has exploited the turmoil to expand in Libya and threaten its oil installations. It has held the coastal oil hub of Sirte since 2015.