The US continued its bombing campaign in Syria as warplanes targeted a dozen oil refineries overnight, killing at least 14 Isis fighters.
Up to five British jihadists, including a teenager from Brighton, are believed to have been among those killed in the air strikes.
Five civilians were also killed in the attacks carried out by America Saudi and United Arab Emirates aircraft, the Syrian Observatory for Human Rights reported.
The campaign continued a day after the US and five Arab allies opened their military operation against Isis (also known as the Islamic State) in Syria with more than 200 strikes on some two dozen targets.
The US military confirmed a total of 13 strikes had targeted 12 so-called small “modular oil refineries”, which are used by Isis to fund its operations, finance its attacks and fuel its vehicles.
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Isis generate about $2 million (£1.2 million) a day in profit from modular oil refineries by producing between 300-500 barrels of refined petroleum per day, a US Department of Defence official said.
Their initial assessment suggested the strikes against facilities in Al Mayadin, Al Hasakah, Abu Kamal and near Dayr az Zawr had been successful.
Speaking after the strikes were confirmed, one US official told Fox News: “This is not going to look like the oil fields burning in Iraq,” in apparent reference to the Gulf War.
The air strikes came as hard-line Syrian rebels who have been battling Isis sought cover, fearing a wider aerial campaign against all fighters seen as a potential threat to the US.
On Thursday, David Cameron warned Britain is ready "play its part" in tackling Isis’ insurgency.
In his speech to the UN General Assembly, the Prime Minister confirmed he will seek approval from parliament for the UK to join coalition countries, led by the United States, unleashing aerial strikes against Isis inside Iraq.
Parliament will be recalled on Friday to discuss if Britain should join in the air strike campaign against Isis targets. Mr Cameron's remarks followed a speech by President Barack Obama, where he similarly set out his arguments for taking on what he called the Isis “network of death”.Reuse content