Members of Libya's U.N.-backed Presidential Council reached Tripoli by ship on Wednesday, defying attempts to keep them out of the city and prevent them
from installing a unity government.
Seven members of the Council including Fayez Seraj, its head and the new government's prime minister, arrived from Tunisia at Tripoli's Abusita naval base amid tight security.
A separate self-declared government also based in Tripoli and armed groups that back it had warned the Council and the unity government not to travel to the capital.
Tripoli's airspace was closed for several hours on Sunday and Monday, a move the Council said was designed to prevent it from reaching Libya.
Seraj told Reuters that the council members had travelled in a Libyan navy vessel from the Tunisian port of Sfax, a 12-hour journey.
"There are challenges ahead of us, including uniting Libyans and healing divisions," he said after arriving.
He later made a brief statement saying the government would release a program in the coming days.
"We will work for a cease-fire across Libya, for national reconciliation and the return of displaced people, and we will seek to confront Islamic State," he said.
The government of national accord (GNA) emerged from a U.N.-mediated deal signed in December aimed at ending the country's political impasse, resolving its armed conflict and tackling a growing threat from Islamic State jihadists.
Western powers have recognized it as Libya's sole legitimate government, but it has faced continuing opposition from hardliners in both eastern and western Libya.
Since 2014 Libya has had two competing pairs of parliaments and governments, both backed by loose alliances of armed brigades. The government in Tripoli was brought to power by armed factions that won a battle for control of the capital in 2014.
Tripoli, home to many such factions, has seen sporadic clashes in the past few days. Early on Wednesday, loud explosions followed by heavy gunfire were heard over the city.
Ahead of its arrival, the Council said it had negotiated a security plan with police and military forces in Tripoli, and with some armed groups.
The road outside the naval base was heavily secured with checkpoints and armored vehicles on Wednesday.
Security forces were also stationed inside the base, and some guards arrived with the Council members.
The Council has called for an immediate transfer of power to the unity government, though both the Tripoli and eastern-based governments oppose this.
The unity government's 18 members have so far failed to secure a vote of approval from Libya's eastern, internationally-recognized parliament, as required under the U.N.-mediated deal, and Fathi al-Mrimi, a spokesman for eastern parliament's president, said its arrival was "premature."
"They have entered by force under foreign protection, and Libyans won't accept anything imposed on them by force," he told Reuters.
U.N. Libya envoy Martin Kobler welcomed the Council's arrival, saying the international community was "ready to provide the required support and assistance", and that all Libyan security actors had a responsibility to ensure its safety.
The EU, as well as the French, British and Italian foreign ministers also greeted the move.
"We stand ready to respond positively to requests for support and assistance from the GNA to help them restore stability to Libya, rebuild the economy, fight Daesh (IS) and tackle the criminal gangs that threaten the security of Libyans and exploit illegal migrants," said British Foreign Secretary Philip Hammond.