The world powers that support Libya's fledgling government urged the country to unite Thursday as rival armed groups jockey for control of its oil exports.

International officials underlined that military faction leader Khalifa Haftar's recent seizure of Libya's main oil ports should not be allowed to undermine peace.

"The oil question should unite and not divide and as of now we here on the right track," Martin Kobler, the UN special envoy to Libya, said after the meeting.

US Secretary of State John Kerry and Italy's Foreign Minister Paolo Gentiloni chaired the talks in New York, where envoys are gathered for the UN General Assembly.

They were joined by representatives of 20 mostly Middle Eastern and European allies, along with the European Union, United Nations, Arab League and African Union.

The powers saluted the leadership of the head of Libya's unity government, Fayez al-Sarraj, but said he should reach out to rivals like Haftar to build consensus.

"This is very crucial at this moment," Gentiloni said. "We know we don't have an easy situation in the country. Sarraj is strengthened by huge international support."

Sarraj described the talks as "constructive and positive" and added: "I'm willing to talk with anyone for the sake of solving the problems of Libyans.

"There are many obstacles of course and one of them is trying to have a unified army under the political body."

Libya has been riven with violence since the dictator Moamer Kadhafi was ousted and killed in 2011, and rival governments now dispute its large oil resources.

A power-sharing Government of National Accord was formed in December 2015 with the backing of the United Nations and recognition of the international community.

The fledgling administration is based in the capital Tripoli, in the west of the country but still needs a vote of confidence from Libya's parliament.

The parliament is based in the east of the country and backs a former government now based there, and both rival regimes rely on a patchwork of militia groups for support.

The eastern parallel government is supported by forces loyal to Haftar, feared by some as a would-be military strongman.

- Unacceptable military developments -

"In recent days there have been unacceptable military developments," French foreign minister Jean-Marc Ayrault told reporters after the meeting.

"For us it's clear that the oil wells should be under the control of the National Oil Corporation and the Sarraj government," he added.

The powers urged the GNA to prepare for elections next year that would endorse a more broad-based administration representative of each and west.

The international ministers also confirmed that GNA forces are the only armed groups in Libya that should receive foreign arms, funding and training.

Last week Haftar's forces seized four export terminals in Libya's coastal "oil crescent," in a blow to the GNA's efforts to extend its writ across the whole country.

Haftar remains in military control of the ports but the National Oil Company, under the GNA, manages them and an export shipment was allowed to set sail on Wednesday.

But fighting and political division have disrupted the industry and NOC chairman Mustafa Sanalla said Thursday that Libya is "on the road to financial collapse."

In New York, the international powers said the NOC and Sarraj's government should remain in charge of the oil.

Meanwhile, GNA forces have been fighting for more than four months to oust the Islamic State extremist group from Sirte, Kadhafi's coastal home town.

But suicide bombings and sniper fire from the cornered jihadists have slowed the offensive, while Haftar's forces have not joined the anti-IS battle.

More than 450 loyalists have been killed and around 2,500 wounded since the operation began in May. Ten IS and three pro-government fighters died Thursday.