US-led airstrikes are continuing against Islamic State-controlled oil fields in Syria, not long after the Pentagon said hydrocarbons were no longer the fundamentalist militant group’s most significant source of financing.

The American-led coalition earlier this week attacked and destroyed “multiple ISIL oil pumps” near Dayr az Zawr, according to a Department of Defense press release issued Monday.

The operations demonstrate that the US is continuing to employ a risky tactic in Syria that it was reportedly reluctant to use after initially launching military operations last September against the Islamic State—one that is likely to be yielding diminishing benefits, according to the Pentagon itself.

On Feb. 3, Defense Department spokesperson Rear Adm. John Kirby said that oil sales were “no longer the main source of revenue” for Islamic State militants.

“They get a lot of donations. They also have a significant black market program going on. But what I can tell you is that we now know that oil is no longer the lead source of revenue,” Kirby said.

The attacks earlier this week were not the first since Kirby publicly revealed the Pentagon’s assessment of the militant-controlled oil industry in Syria. On Feb. 12, the anti-Islamic State coalition also struck “multiple ISIL oil pump jacks” near Hasakah, according to a Pentagon statement. A few days earlier, the US-led alliance took out “an ISIL mobile oil rig” in the proximity of the same city, the Defense Department said.

Last month, American officials boasted for the first time that coalition forces have attacked at least 200 Islamic State controlled-oil wells, as The Sentinel reported.

They did not note, however, that oil infrastructure is only being targeted in Syria because the nature of the operations remain controversial. Similar facilities in Iraq are not on the receiving end of US-led attacks, because “the government in Baghdad has asked the US not to hit oil infrastructure,” according to The Guardian.

The US military and its allies were initially concerned about targeting oil fields in Syria because they did not want to destroy “underground resources belong[ing] to the Syrian people” while doing “long-term damage” in both economic and environmental terms, Foreign Policy’s Keith Johnson reported in September. Johnson recalled the images of “choking, black fires that came from burning oil wells sabotaged by Saddam Hussein’s forces in the first Gulf War” in detailing concerns about the lasting damage such attacks can do.