Supporters of a government endorsed by Libya's parliament and by an eastern-based military strongman had tried to move into the western city of Tripoli by force.

That sparked pre-dawn clashes with armed groups supporting interim Prime Minister Abdulhamid Dbeibah.

Hours later they pulled out, citing the "security and safety of citizens", as the United Nations, European Union and United States appealed for calm.

There were no immediate reports of casualties from the fighting, but AFP correspondents saw burned-out cars and military convoys on a major thoroughfare later Tuesday morning.

Dbeibah was appointed under a troubled UN-led peace process early last year to lead a transition to elections set for December, but the vote was indefinitely postponed.

In February this year, the eastern-based parliament appointed rival premier and former interior ministry Fathi Bashagha to take his place, arguing that Dbeibah's mandate had ended.

Dbeibah has refused to hand over power except to an elected administration.

Both men are from the western city of Misrata and are backed by different armed groups in the capital.

Bashagha's press service had announced overnight "the arrival of the prime minister of the Libyan government, Mr Fathi Bashagha, accompanied by several ministers, in the capital Tripoli to begin his work there".

But his arrival sparked a battle that raised fears of a return to the chaos that followed a 2011 revolt that toppled dictator Moamer Kadhafi -- and to the all-out conflict that gripped the capital when pro-Haftar forces attacked in 2019-20.

Several hours later, Bashagha's camp announced that he and his ministers had "left Tripoli to preserve the security and safety of citizens".

Dbeibah's defence ministry said it would respond "with an iron fist" to anyone "attacking security and the safety of citizens".

- Bashagha support 'tanked' -

Local media later broadcast footage of Dbeibah meeting members of the public in the streets of the capital.

The education ministry announced that schools would be closed for the time being.

Libya expert Emadeddin Badi said Bashagha's move had been "a failed attempt at a fait accompli".

Badi said Bashagha had "lost a large proportion of his constituency in his hometown of Misrata, tarnished his anti-crime brand and now tanked his popular support."

"It'll be difficult to pick up the pieces after this," he tweeted.

The UN's top in-country official, Stephanie Williams, in a tweet urged all sides to maintain calm, including avoiding "inflammatory rhetoric".

Bashagha, in video footage broadcast by Libyan television stations, said he would deliver a "unity speech to the Libyan people" on Tuesday evening.

His interior minister Issam Abu Zariba pledged that their administration would assume its duties "peacefully" and "in compliance with the law".

He called on "all security forces and concerned parties to cooperate" in ensuring a smooth transition.

Pro-Bashagha armed groups had already deployed in March on the edges of the capital, raising fears that a fragile ceasefire in place since October 2020 would collapse.

- 'Very worrying' -

The creation of two governments echoes Libya's troubled period of rival administrations between 2014 and 2021, when the nation was ripped apart by civil war.

The revolt that toppled Kadhafi plunged the vast but sparsely populated country into violence as armed groups vied for control and a string of interim governments came and went.

Many have been integrated into the state, partly to access a share in the country's vast oil wealth, and rights groups have accused all sides of abuses.

Bashagha is backed by Haftar, who led a failed bid to seize Tripoli in 2019-20 and is widely hated in the capital.

EU foreign affairs chief Josep Borrell said Tuesday the situation had become "very grave".

"We were expecting something like this to happen because in Libya we had not elections but we have two governments," he said. "And sooner or later, when there are two governments, they clash."

The US embassy urged "all armed groups to refrain from violence and for political leaders to recognise that seizing or retaining power through violence will only hurt the people of Libya".

The American mission also urged progress toward presidential and parliamentary elections.