The United States called Tuesday for an immediate resumption of Libya's lifeline oil exports that have been blocked by forces loyal to military strongman Khalifa Haftar since last week.

"The suspension of National Oil Corporation (NOC) operations risks exacerbating the humanitarian emergency in #Libya and inflicting further needless suffering on the Libyan people," the US embassy in Tripoli tweeted.

"NOC operations should resume immediately," it said.

Haftar's forces, at war with fighters loyal to the UN-recognised Government of National Accord, blocked oil exports from Libya's main ports on Saturday, a day before an international peace conference.

The move to cripple the country's main income source was a protest against Turkey's decision to send troops to shore up Haftar's rivals.

The action has suspended operations from Libya's "oil crescent", blocking several export terminals including Brega, Ras Lanuf and Al-Sidra ports.

"The storage capacity of these ports is limited and the NOC will be obliged to put a complete halt to crude production once maximum capacity has been reached," the oil company said Monday.

Libya's 'oil crescent' is a vital source of revenue for the North African country
Libya's 'oil crescent' is a vital source of revenue for the North African country AFP / Abdullah DOMA

The NOC said Libya's daily crude output of 1.3 million barrels a day would be virtually wiped out, translating into losses of $77 million a day.

According to industry experts, Washington also opposes the suspension of Libyan crude exports because of the impact on the world oil market.

Hamish Kinnear, an analyst at risk consultancy Verisk Maplecroft, said Haftar's action was a "blunt reminder" that his forces control most of Libya's oil and gas resources.

"The fact that the shutdown coincided with the Berlin conference, a high-level Libya peace summit... is no coincidence," he said.

"By shutting the fields, Haftar was making it clear that he holds a veto over any proposed ceasefire agreement or eventual political agreement."

World leaders at the Berlin conference, in a final declaration on Sunday, said they opposed "hostilities against all oil facilities and infrastructure" in Libya.

The oil-rich North African country has been torn by fighting between rival armed factions since a 2011 NATO-backed uprising killed dictator Moamer Kadhafi and toppled his regime.

Libya