Libya's National Oil Company says it is preparing to resume exports of crude, halted for months because of political differences and attacks by Islamist militants.

"Now we will begin working... to restart exports from the ports that were closed and from the fields that supply them," the NOC said in a statement Sunday.

Last week, oil installation guards announced the reopening of two major export terminals after an agreement with the Tripoli-based Government of National Unity (GNA).

Ras Lanuf and Al-Sidra terminals, with respective capacities of 200,000 barrels per day and 500,000 bpd, have been closed since January after storage tanks were set on fire during attacks by the militant Islamic State group.

The NOC said the GNA had decided to release funds to allow the oil company "to boost production by over 900,000 bpd by the end of the year 2016".

Libya's oil sector, its main source of income, is managed by the NOC which is split into two rival branches.

The main branch is in the capital and allied to the GNA, but its rival in the east is close to a parallel executive that has the confidence of parliament which has so far refused to cede power to the internationally recognised Tripoli government.

Nagi al-Maghrabi of the eastern-based NOC told AFP that he rejected the deal between the GNA and the oil installation guards, however.

"We will not accept that oil is exported under these conditions... as there will be no guarantees of the fair distribution of income, or assurances that the funds will not fall into the hands of militias," he said.

Oil is Libya's main natural resource with reserves estimated at 48 billion barrels, the largest in Africa.