TRIPOLI, Libya (AP) — The head of a U.N.-brokered Libyan unity government arrived in the capital by sea Wednesday, March 30, with six deputies to set up a temporary seat of power in a naval base despite threats from competing factions.

Western nations view the unity government as the best hope for ending Libya’s chaos and uniting all factions against an increasingly powerful Islamic State affiliate, which has seized the central city of Sirte. But factions within Libya’s two rival governments, one of which is based in Tripoli, are opposed to the U.N.-backed body.

Fayez Serraj sailed in from neighboring Tunisia aboard a Libyan vessel, according to the unity government’s website, which denied reports that the officials had been brought in aboard an Italian ship.

The six deputies are members of the Presidential Council, which was established based on a U.N.-mediated deal signed by splintered groups from the two governments last year. The council formed the new unity government headed by Serraj.

The officials were prevented from flying into Tripoli by a rival Islamist-backed government based in the capital. A third government is based in the east of the vast oil-rich country. Libya has been dominated by an array of militias since the 2011 uprising that toppled and killed longtime dictator Moammar Gadhafi.

“It is time for all of us as Libyans to work together for the sake of Libya,” Serraj said upon his arrival, according to the government’s Facebook page. He urged rivals to “turn the page of the past,” saying “revenge, alienation, antipathy, and hatred don’t build a state.”

He also vowed to unify Libyan state institutions and implement “rapid measures” to lessen the suffering of civilians. Pictures on the website showed him shaking hands with naval officers, who presented him with a golden plate.

Ali Abu Zakouk, the foreign minister of the Islamist-backed government, said Serraj’s presence is “unacceptable.” Last week, the Tripoli government declared a state of emergency and ordered its forces to “increase security patrols and checkpoints.”

The U.N. envoy to Libya, Martin Kobler, praised Serraj’s “exceptional personal courage” and urged officials to facilitate an “immediate orderly and peaceful handover of power.” He tweeted: “All security actors in #Libya have responsibility to ensure safety and security of Presidency Council & #GNA.”

State Department spokesman John Kirby said Tuesday that the United States “is deeply troubled by reports that a small group of political obstructionists have closed the air space around Tripoli in a deliberate attempt to prevent the Libyan Government of National Accord from arriving,” calling such actions “reprehensible.”

But even with international support, Serraj faces a daunting array of challenges, and could struggle to impose his will on the Central Bank, the state-run oil company and other institutions.

He is also at risk of being attacked or besieged in his base by rival militias. He is being guarded by battle-hardened militias from the city of Misrata, which saw fierce fighting during the uprising five years ago. But Tripoli is also home to several powerful Islamic militant groups, which could move against him, setting off yet another round of fighting.

The U.S. and its European allies hope the unity government can unify the country and serve as an ally against the Islamic State group. U.S. special forces have been on the ground, working with Libyan officials, and U.S. warplanes have carried out airstrikes. Libyan officials say small teams of French, British and Italian commandos are also on the ground helping militiamen battling IS in the eastern city of Benghazi, though those three countries have not confirmed their presence.

The establishment of a unity government could pave the way for lifting an arms embargo on Libya, allowing Western countries to provide greater support to local forces.