The US-led coalition has targeted oil refineries in Syria during a third night of air strikes against Islamic State (IS) militants.
The raids - carried out by US, Saudi and UAE aircraft - killed 14 IS fighters and five civilians in eastern Syria, activists said.
The US military said the refineries generated as much as $2 million (£1.2m) per day in revenue for IS.
US President Barack Obama has vowed to dismantle the IS "network of death".
IS has seized large areas of Syria and Iraq in recent months and controls several oilfields. Sales of smuggled crude oil have helped finance its offensive in both countries.
The US has launched nearly 200 air strikes against the militants in Iraq since August and expanded the operation against IS to Syria on Monday.