WASHINGTON (AP) — The U.S. Treasury Department says Islamic State militants are earning about $1 million a day just from black market oil sales.

The official who leads the department’s effort to undermine the group’s financial strength says IS also has taken in at least $20 million in ransom payments this year from kidnappings.

David Cohen, the Treasury undersecretary for terrorism and financial intelligence, says the group takes in several million dollars a month from wealthy donors, and from extortion rackets and other criminal activities, such as robbing banks.

Cohen says that except for state-sponsored terrorist groups, the Islamic State group is probably the best-funded terrorist organization the Treasury Department has ever confronted.

THIS IS A BREAKING NEWS UPDATE. Check back soon for further information. AP’s earlier story is below.

Islamic State militants are amassing wealth at an unprecedented pace, earning about $1 million a month from black market oil sales alone, a Treasury Department official said Thursday.

David Cohen, who leads the department’s effort to undermine the Islamic State group’s financial strength, said the extremists also get several million dollars a month from wealthy donors, and from extortion rackets and other criminal activities, such as robbing banks. In addition, he said the group has taken in at least $20 million in ransom payments this year from kidnappings.

“It is difficult to get precise revenue estimates on the value to ISIL of these transactions in light of the murky nature of the market, but we estimate that beginning in mid-June, ISIL has earned approximately $1 million a day from oil sales,” Cohen said, using an acronym for the group.

The group wants to create a caliphate, or Islamic empire, in the Middle East. Led by Iraqi militant Abu Bakr al-Baghdadi, the Islamic State group initially tried to oust Syrian President Bashar Assad, but other groups, including al-Qaida central command, turned against IS because of its brutality.

IS has captured territory across Syria and northern Iraq.

“With the important exception of some state-sponsored terrorist organizations, IS is probably the best-funded terrorist organization we have confronted,” Cohen, undersecretary for terrorism and financial intelligence, said in prepared remarks for a speech at the Carnegie Endowment for International Peace.

Unlike the core al-Qaida terrorist network, IS gets only a relatively small share of funding from deep-pocket donors and therefore does not depend primarily on moving money across international borders. Instead, IS obtains the vast majority of its revenues through local criminal and terrorist activities, Cohen said.

“They rob banks. They lay waste to thousands of years of civilization in Iraq and Syria by looting and selling antiquities,” he said. “They steal livestock and crops from farmers. And despicably, they sell abducted girls and women as sex slaves.”