The US and a coalition of Arab allies have launched fresh airstrikes targeting an Islamic State-controlled oil well in Syria.

The raids struck southwest of the Syrian town of Albu Kamal, close to the border with Iraq, according to the UK-based Syrian Observatory for Human Rights.

In recent days the US-led raids have been targeting oil refineries in eastern Syria, which are a rich source of revenue for the group.

At least 14 militants and five civilians were killed in strikes overnight.

Backed by France, the US has also been carrying out strikes against IS targets in Iraq, with the UK expected to follow suit after a Parliamentary vote on Friday.

The latest attacks come as FBI Director James Comey said the bureau has identified the IS militant accused of beheading two American journalists, James Foley and Steven Sotloff, and British aid worker David Haines.

Meanwhile, US officials appear to have been taken by surprise by reports that IS is planning attacks on US and French subways.

A senior Obama administration official has said no one in the US Government is aware of the apparent plot, which was made public by the Iraqi Prime Minister on the sidelines of the UN General Assembly in New York.

Haider al Abadi did not specify a location in the US for the supposed attack.

He told a small group of US reporters: "Today, while I am here, I am receiving accurate reports from Baghdad where there was arrest of few elements and there are networks planning from inside Iraq to have attacks.

"They plan to have attacks in the metros of Paris and the US," he added. "From the details I have received, yes it looks credible."

In an interview with CNN, US Deputy Assistant Secretary of State Brett McGurk said he attended a meeting between Vice President Joe Biden and Mr al Abadi on Thursday, and that Mr al Abadi told them there is "no specific credible threat whatsoever that they have uncovered to the United States".

The White House said the meeting was planned last week and not related to Mr al Abadi's remarks about the purported plot.

US and European leaders have voiced concerns that IS might send jihadists with Western passports home to launch terrorist attacks.

US President Barack Obama called on Wednesday for the world to join together to destroy the group, which he branded a "network of death".

With Western nations becoming increasingly galvanised to join the fight against IS, Iran has urged the West to take responsibility for its role in allowing extremism to flourish.

Speaking at the UN General Assembly earlier, Iran's President Hassan Rouhani said the West had helped create "terror havens" in parts of the Middle East and Central Asia.