The US embassy serving Libya has warned that the shutdown of the country's oil fields risks worsening the humanitarian emergency there.

An embassy statement called for the immediate resumption of production.

Libya's state-run, National Oil Corporation says the forces of the rebel commander, General Khalifa Haftar, have in recent days halted oil field operations in the east and south.

Oil exports - the backbone of the economy - have plummeted.

General Haftar's forces are besieging the capital, Tripoli - where Libya's UN-backed government is based. He's declined to sign a ceasefire agreement that would consolidate a fragile truce.