The US envoy to Libya has said Washington will support the resumption of oil exports from the politically divided country if revenues go to the UN-backed unity government.

"The key is that oil won't be diverted to anyone else other than the... recognised government of Libya," Jonathan Winer told AFP on Wednesday, referring to the Tripoli-based Government of National Accord (GNA).

Winer was speaking from Washington after forces loyal to a rival authority in eastern Libya seized four key ports in the country's so-called "oil crescent" this week and handed them over to the National Oil Company.

On Thursday, the NOC announced an "immediate" resumption of oil exports from two of those ports.

"Oil needs to be produced throughout the country to generate the revenues necessary to pay for salaries for the Libyan people to have the government be able to function and to be able to" provide services, Winer said. 

The oil "has to be exported according to lawful contracts with the proceeds going into the central bank of Libya whose main offices are in Tripoli," he added.

"If the oil is going in the government's revenues and the government supports that, there is no action for the international community to take," he said.

But "if oil were to be diverted towards any particular group, new bank accounts to be set up, oil being sent to parties who have not had contracts for the oil already... the US will seek to enforce UN Security Council resolutions," Winer said.

If the GNA asked for international support to prevent oil from being exported, he said, the international community was "likely to provide that support".

Libya has been in turmoil, with rival administrations and militias fighting for control of the oil-rich country since the 2011 revolt that ousted longtime dictator Moamer Kadhafi.

The unity government has been working in Tripoli since March, but has struggled to assert its control over the country, which with an estimated 48 billion barrels holds Africa's largest oil reserves.

US warplanes are supporting pro-GNA forces in a battle to expel the last Islamic State group jihadists from the coastal city of Sirte, previously their North African stronghold, west of the oil crescent.

The jihadists seized Sirte in June last year.

"The US does not want Libyans fighting with other Libyans," said Winer. "We want Libyans to unite to fight the security threats."

"We think it's the right thing for the Libyans to talk rather than to fight with one another," the US envoy added.

Source: AFP