LONDON: Libya's oil production has been reduced to 315,000 barrels per day (bpd) as storage tanks at Hariga and Zueitina ports fill up due to eastern officials blocking exports, two Libyan oil sources said on Saturday.

The production drop has been gradual as ships have been barred from loading at the ports since Thursday.

Some two-thirds of storage capacity at eastern ports is out of action and the remaining capacity is nearly full, one of the sources said.

Storage at oil fields is also limited due to attacks by Islamic State militants in previous years.

Libya had been producing more than 1 million bpd in recent months, but on June 14 an attack against forces loyal to eastern-based commander Khalifa Haftar at the ports of Ras Lanuf and Es Sider shut them down, slashing production by 450,000 bpd.

After recapturing the ports, Haftar's Libyan National Army (LNA) announced it would be handing them to a parallel National Oil Corporation (NOC) in the eastern city of Benghazi, which said it would stop exports under the internationally recognised NOC in Tripoli, raising the prospect of prolonged output losses.

The Tripoli NOC has said it expects to declare force majeure on exports from Zueitina and Hariga on Sunday, bringing total production losses to 800,000 bpd.

Port sources said there was no change to the situation on Saturday, with tankers booked by the NOC in Tripoli still blocked from loading.

Western powers have called for the ports to be returned to the exclusive control of NOC Tripoli. Past attempts by eastern-based factions to sell oil independently of Tripoli have been thwarted by U.N. Security Council resolutions.