Seraj and six deputies disembarked after a 12-hour voyage from Tunisia at Tripoli's Abusita naval base on Wednesday, despite warnings to leave from a separate self-declared administration already located in the fractious capital.

As heavy gunfire echoed across Tripoli, the UN envoy to Libya, Martin Kobler, praised Seraj's "exceptional personal courage" and urged Libya's factions and militias to ensure a "peaceful handover of power" in the vast, oil-rich country.

Guarding Seraj were militias from Misrata, which saw fierce fighting in 2011 when dictator Muammar Gadhafi was ousted and killed. Checkpoints outside the Tripoli naval base were heavily secured on Wednesday.

The new government's social media page show naval officers presenting a golden plate to Seraj (pictured above), who heads the new government's Presidential Council while also being its prime minister.

Establishment of the unity government, forged late last year at UN-led talks in Morocco, could prompt the lifting of an international arms embargo and "nation building" support from Western nations.

Arrival welcomed by UN, EU

Seraj's arrival was welcomed by the EU as a step toward establishing stability, also seen as needed to restrain smugglers accused of exploiting boat migrants heading to Europe across the Mediterranean toward Italy.

Khalifa Ghweil, the head of the rival Tripoli administration said Seraj's arrival was "unacceptable." On Tuesday, he had accused the UN of "deepening the schism."

US State Department spokesman John Kirby - in an apparent reference to Ghweil's faction - accused a "small group of political obstructionists" of having closed airspace around Tripoli since Sunday to deter the unity team's arrival.

Reuters said various militias appeared to be leaning toward supporting Seraj, 56, a trained architect who comes from a well-known family originating from Tripoli.

A powerful unit called the Special Deterrent Force said it would support the new government of national accord (GNA), which has 18 members in all.

"We want one man to unite the country. We hope this man is Seraj," said unit spokesman Ahmed ben Salem.

He added that some 20 percent of militias were opposed to the new government.

Arrival 'premature'

So far, the unity government has also failed to secure approval from Libya's eastern, internationally-recognized parliament, as required under December's UN-mediated deal.

The GNA's arrival was "premature," said Fathi al-Mrimi, a spokesman for the eastern parliament based in Tobruk.

"They have entered by force under foreign protection, and Libyans won't accept anything imposed on them by force," he added.

Seraj vowed to stabilize state institutions, including the central bank and state-owned oil operations, and "rapid measures" to lessen the suffering of civilians.

In a nod to Islamist factions, he stressed that laws passed by the GNA would be compliant with Shariah.

Rumor - foreign commandoes

Libyan officials quoted by Associated Press said small teams of French, British and Italian commandoes were inside Libya, helping militiamen to battle "Islamic State" jihadists who have a foothold in the eastern city of Benghazi.

Neither France, Britain nor Italy have confirmed the presence of such special forces.