United States officials have confirmed that the vicious Islamic State has fast become one of the world's wealthiest terror groups, generating tens of millions of dollars a month, largely through black market oil sales, along with ransoms and extortion.
The Islamic State, also known variously as the ISIL, ISIS or just IS, sells oil from territory it controls in Syria and Iraq to Turkish middlemen, Iraqi Kurds and even the Syrian government of President Bashar Assad, according to the Obama administration's point man on terrorist financing.
Before the United States began targeting refineries in militant-occupied areas of Syria last month, the Islamic State group was making about $1 million a day from oil sales, US Treasury Department undersecretary David Cohen said on Thursday.
Its total income of "millions of dollars per month" from oil, kidnapping ransom and extortion in occupied areas, and the speed with which it has amassed funds, make the militant group unlike any other terrorist entity the US has confronted, he said.
The group also differs from other organisations, including al-Qaeda, in that a "relative small share" of its income is derived from sympathetic individuals in the Arab world. It does not "depend principally on moving money across international borders", making it far more difficult to use international tools to stem the flow of funds.
"As with the rest of the campaign against ISIL, our efforts to combat its financing will take time," he said, using one of several acronyms that refer to the Islamic State militants. "We have no silver bullet, no secret weapon to empty ISIL's coffers overnight."
While most of the attention has been focused on the hundreds of air strikes the United States and partner nations have conducted against Islamic State targets in Iraq and Syria in recent weeks, the administration has sought to emphasise that its strategy also includes efforts to undermine the group's finances.
Black money from oil
Oil sales have been a particular concern. "As of last month, ISIL was selling oil at substantially discounted prices to a variety of middlemen, including some from Turkey, who then transported the oil to be resold," Cohen said.
"It also appears that some of the oil emanating from territory where ISIL operates has been sold to Kurds in Iraq and resold into Turkey."
The Assad government in Syria, he said, has also "made an arrangement to purchase oil from ISIL."
The $1 million-a-day assessment of militant oil income predates US airstrikes against oil refineries and other facilities in Islamic State-controlled territory in Syria.
The group has also made at least $20 million this year alone in kidnapping for ransom, Cohen said. France and other European countries have reportedly sanctioned massive payments for their nationals who have been released by the militants, while the United States and Britain have adopted policies of non-payment.
Cohen also noted that "scores of bank branches are located in territories where ISIL operates" in Iraq and Syria and said that the international community is working to limit the group's ability to conduct transactions through banking systems in those countries and internationally.
His remarks came as dramatic pictures emerged showing the moment an attempt by IS militants to retake a hill near Kobane was stopped by an allied air strike.
Tel Shair is the mountain overlooking Kobane on the Syrian side of the Turkish border, and has been fought over for weeks. It was taken by IS militants two weeks ago, and retaken by Kurdish fighters on October 14 after US-led air strikes helped turn the tide of battle.
On Thursday morning, IS fighters made a sudden surge up the hill, driving the Kurds off it and planted their now well-known black flag. As night fell, though, an air strike made a direct hit, sending a ball of flame up in the air and the jihadists running down the hill again.
"With the current air strikes that are going on in support of the Kurdish fighters who know the town, the line has kind of stabilised," one US defence official said.
However a US military official, also speaking on condition of anonymity, said it was too soon to say whether the resupply of weapons would make a difference.