Italy's foreign minister flew into Tripoli on Tuesday for talks with the head of the unity government Fayez Seraj - the first senior Western official to meet the new Libyan administration since it moved to the capital.
The mission by Italy, Libya's former colonial ruler, will be seen as a vote of confidence in Seraj, who arrived in the city last month at the head of a UN-backed Presidential Council to try and end years of political deadlock and conflict.
Seraj was due to meet Italy's Paolo Gentiloni at a heavily secured naval base.
Italy, France and other Western powers have offered to support Seraj and train security forces facing a growing threat from Islamist militants.
The reopening of diplomatic missions could eventually pave the way for the return of international oil industry staff, though some of Libya's major oil facilities have recently come under attack from Islamic State militants.
Western diplomatic staff were evacuated from Tripoli in 2014 amid heavy fighting between rival factions.
The unity government is meant to replace two rival sets of governments and parliaments in Tripoli and the east. Both were backed by loose alliances of the armed factions that established themselves after the uprising that toppled Muammar Gaddafi in 2011.
