UN special envoy Bernardino Leon visited Tobruk on Monday in a show of support for Libya's elected parliament, the House of Representatives.
The move comes as a rival assembly was set up by armed groups that took control of Tripoli last month.
The House was elected in June and its previous name, the General National Congress (GNC), was scrapped because many Libyans associated it with political chaos; the alliance controlling Tripoli has, however, reinstated the GNC.
Samir Ghattas, a spokesman for the U.N. Mission in Libya, said:
"The legitimacy lies only with the House of Representatives which won legitimate elections ... We want a political solution and are against the use of violence."