Citing ongoing US efforts to escalate their attacks on ISIS, Secretary of Defense Ash Carter says the US is reviewing its rules of engagement in the war and expanding their list of legitimate targets to allow for more strikes against ISIS-related targets.

Carter cited a recent flurry of US airstrikes against fuel trucks in ISIS territory as an example of “changing tactics” in the war. Officials are hoping that the attacks on fuel trucks will put further pressure on the economy of the ISIS “caliphate,” part of an effort to cripple the region’s fuel exports.

While this has had some success, it is also seen as a very risky tactic, as damaging the economy in ISIS-occupied territory risks making the average civilian within even more dependent on the cash-rich ISIS movement, and more vulnerable to recruitment.

The US has been escalating airstrikes intermittently since beginning their strikes against ISIS targets last year, and is constantly looking for new targets. Though there has been a flurry of activity since last week’s Paris attacks, they have mostly hit empty buildings.