Libyan forces opposed to the country's internationally recognized government have warned  it that any attempts to export oil independently would force them to take military action to intervene and seize oil ports and facilities.

The conflict over oil is intensifying in Libya, where two rival governments, each backed by loose coalitions of ex-rebels who once fought together to oust Muammar Gaddafi, are battling for control of the North African OPEC producer.

Forces with Prime Minister Abdullah al-Thinni's official government hold two key oil ports, Ras Lanuf and Es Sider, and he said over the weekend he would seek independent oil sales and open a bank account overseas to hold revenues.

Responding to the announcement, Ismail Shikri, a spokesperson for forces allied with the rival Tripoli government, said any attempt by Thinni to sell oil by bypassing the central bank and the National Oil Corporation (NOC) would trigger military action.

"Selling of oil beyond the Tripoli-based NOC is considered zero hour for our forces to launch a military operation by using all the means," Shikri said.

Tripoli-allied forces in December tried to retake the two major ports, which have a combined export capacity of 600,000 barrels a day.

Fighting closed the ports since then and a force majeure is still in place.

Late last month, an official said Tripoli-allied brigades pulled back from positions around Ras Lanuf and Es Sider to fight Islamist militants, raising hopes the two terminals would soon reopen.

Ras Lanuf and Es Sider are controlled by federalist forces now allied to Thinni.

But a year ago, those same forces tried to ship crude independently, leading to a standoff with the government and a US special forces raid to stop a tanker.

Nearly four years after the NATO-backed civil war ousted Gaddafi, Libya is in turmoil, with conflict opening on several fronts.

Those include attacks by militants tied to the Islamic State, which is taking advantage of the chaos.

Until now, oil sales and revenues have gone through Libya's central bank and NOC in Tripoli.

Several oilfields as well as the ports are closed due to fighting.

Tripoli-based NOC has tried to stay out of the conflict between the rival governments.

Thinni's government has already appointed its own NOC chief based in the east. But analysts said Thinni's government may struggle to convince international traders it is legally entitled to claim ownership of Libyan crude, and thousands of contracts, documents and maps are stored in the Tripoli headquarters of the NOC.