New US and coalition airstrikes have targeted ISIS-held oil refineries in Syria.
The raids killed 14 ISIS fighters and five civilians in eastern Syria, activists said.
The US military said the refineries generated as much as $2 million per day in revenue for ISIS.
President Barack Obama has vowed to dismantle the ISIS “network of death”.
ISIS 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 ISIS to Syria on September 22.
On September 24, the UN Security Council adopted a binding resolution compelling states to prevent their nationals joining jihadists in Iraq and Syria.
President Barack Obama chaired the session and said nations must prevent the recruitment and financing of foreign fighters.
The US military said the fresh air strikes, using fighter jets and drones, hit “small-scale” refineries that were producing “between 300-500 barrels of refined petroleum per day”.
“We are still assessing the outcome of the attack on the refineries, but have initial indications that the strikes were successful,” the US Central Command said in a statement.
The UK-based Syrian Observatory for Human Rights, an activist group that monitors the Syrian conflict, said the strikes killed 14 ISIS fighters in Deir al-Zour and five civilians in Hassakeh.
The US says more than 40 countries have offered to join the anti-ISIS coalition.
France said its fighter jets were carrying out air strikes in Iraq again on Thursday, a day after the beheading of a French hostage in Algeria by an IS-linked jihadist group.
The French military has been carrying out air strikes in Iraq since last week but has not taken part in anti-IS operations in Syria.
On September 24, the Dutch government said it was deploying six F-16 fighter to join the US-led air campaign.
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