The US-led coalition against Islamic State (IS) has targeted 12 oil refineries in Syria on a third night of air strikes against the militants.
Raids carried out by US, Saudi and UAE aircraft killed 14 of the group's fighters and five civilians in eastern Syria, activists said.
According to the Pentagon, the refineries generated up to $2m (£1.2m) per day in revenue for the militants.
In northern Syria, Kurdish forces say they have pushed back an IS advance.
US President Barack Obama has vowed to dismantle the IS "network of death".
Islamic State (IS) oil production
- IS is believed to control six out of 10 of Syria's oil fields, including the Omar facility, and four small fields in Iraq, including Ajeel and Hamreen
- Production in Syria is estimated at 50,000 barrels per day and 30,000 in Iraq, generating revenue of between $1m (£600,000) and $5m per day
- Oil is sold to local merchants, or to middlemen who smuggle it into Iraqi Kurdistan or over borders with Turkey, Iran and Jordan, and then sell to traders in a grey market; oil is also sold to the Syrian government
- Seizures of smuggled fuel in Turkey rose from 35,260 tons in 2011 to more than 50,000 tons in the first six months of 2014, before the Turkish authorities began to crack down on illegal trade
Sources: Financial Times, EIA, Iraq Energy Institute, Maplecroft
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.
In other developments:
- The Netherlands has advised its soldiers not to wear uniform in public while travelling on public transport as a precautionary measure as the Dutch prepare to deploy six F-16 fighters to join the US-led air campaign
- Syria's army said it had retaken the key strategic town of Adra, north-east of Damascus, which had been held by militants from the Nusra Front among others
- France launched air strikes on IS targets in northern Iraq - its first there in nearly a week - and pledged more support for opposition forces in Syria
- IS publicly killed a human rights lawyer, Samira Salih al-Nuaimi, in the Iraqi city of Mosul after convicting her of apostasy, the UN announced
Ten fighters from the UAE and Saudi Arabia joined six US jets to carry out Wednesday night's strikes, the Pentagon said.
The strikes 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.
Pentagon spokesman Rear Adm John Kirby said the purpose of the strikes was "not necessarily to kill militants" but to destroy the facilities, which were funding IS through the black market.
He said the Pentagon was looking into reports that civilians had been killed in coalition air strikes.
Planes came "with a terrifying sound and red lights before the explosions", said one activist quoted by AP news agency.
The strikes killed 14 IS fighters in Deir al-Zour and five civilians in Hassakeh, according to the UK-based Syrian Observatory for Human Rights, an activist group that monitors the Syrian conflict.
Kurdish forces said they had pushed back IS fighters near the Syrian town of Kobane, close to the border with Turkey.
There are reports of heavy gunfire outside the town, and Kurdish commanders have again called for coalition air strikes on IS positions in the area.
IS had besieged Kobane for several days, taking control of the surrounding villages and forcing more than 140,000 Syrian Kurds to flee into Turkey.
The BBC's Mark Lowen, who is on the Syria-Turkey border, says some of those Kurds are now trying to return to Kobane to fight with the Kurdish militia.
Turkey has been overwhelmed by an estimated 1.5 million Syrian and Iraqi refugees since the conflict in Syria between opposition forces and Syrian President Bashar al-Assad began three years ago.
On Wednesday, the UN Security Council adopted a binding resolution compelling states to prevent their nationals joining jihadists in Iraq and Syria.
The US says more than 40 countries have offered to join the anti-IS coalition.
UK Prime Minister David Cameron has said the British military is ready to "play its part" in the fight against IS and the UK Parliament has been recalled to discuss plans for air strikes.
- Formed out of al-Qaeda in Iraq (AQI) in 2013, IS first captured Raqqa in eastern Syria
- It captured broad swathes of Iraq in June, including Mosul, and declared a "caliphate" in areas it controls in Syria and Iraq
- Pursuing an extreme form of Sunni Islam, IS has persecuted non-Muslims such as Yazidis and Christians, as well as Shia Muslims, whom it regards as heretics
- Known for its brutal tactics, including beheadings of soldiers, Western journalists and aid workers
- The CIA says the group could have as many as 31,000 fighters in Iraq and Syria