Washington (CNN)– The top U.S. commander for the fight against ISIS on Monday slammed the idea of “carpet bombing” the terror group.

Army Lt. Gen. Sean MacFarland, who directs the coalition fighting ISIS in Iraq and Syria, provided the most detailed military criticism to date about the concept and detailed why it’s militarily unacceptable.

“Indiscriminate bombing where we don’t care if we are killing innocents or combatants is just inconsistent with our values,” he said in response to a question from CNN on the possibility of using carpet bombing.

Though MacFarland didn’t mention any political candidates by name in his answer, Republican Sen. Ted Cruz of Texas while on the campaign trail has called for employing the practice against ISIS.

“We are the United States of America, and you know we have a set of guiding principles and those affect the way we, as professional soldiers, airmen, sailors marines conduct ourselves on the battlefield,” MacFarland said at a news conference from his Baghdad headquarters held before the Iowa caucuses. “We are bound by the laws of armed conflict. And you know at the end of the day, it doesn’t only matter if you win, it matters how you win.”

MacFarland noted that the Russians have been accused of indiscriminate bombing, killing large numbers of civilians in northwest Syria.

“Right now we have the moral high ground and I think that’s where we need to stay,” he said.

The notion of defeating ISIS by massive imprecise bombing in Iraq and Syria has been brought up several times during the Republican presidential race, with Cruz a particular advocate for the approach.

At December’s GOP debate, CNN’s Wolf Blitzer asked Cruz: “You have said you would, quote, ‘carpet bomb ISIS into oblivion,’ testing whether, quote, ‘sand can glow in the dark.’ Does that mean leveling the ISIS capital of Raqqa in Syria, where there are hundreds of thousands of civilians?”

Cruz responded, “What it means is using overwhelming air power to utterly and completely destroy ISIS.”

He also said, “You would carpet bomb where ISIS is — not a city, but the location of the troops. You use air power directed — and you have embedded special forces to (direct) the air power. But the object isn’t to level a city. The object is to kill the ISIS terrorists.”

He then referred to the Persian Gulf War with roughly 1,100 air attacks a day.

“We carpet bombed them for 36 days, saturation bombing, after which our troops went in and in a day-and-a-half mopped up what was left of the Iraqi army,” he said.

But military analysts note that the first Gulf War was the beginning of the growing use of precision-guided weapons. And in that war, unlike the fight against ISIS, the U.S. was going against Iraqi leader Saddam Hussein’s large numbers of conventional armed troops in the field — readily detectable targets separate from civilian populations.

Cruz was asked again about the idea in the Fox News debate last week, answering, “You know, you claim it is tough talk to discuss carpet bombing. It is not tough talk. It is a different, fundamental military strategy than what we’ve seen from (President) Barack Obama.”

Fellow Republican candidate Donald Trump, for his part, has said that he would kill the families of terrorists in order to win the fight against ISIS.

“When you get these terrorists, you have to take out their families. They care about their lives, don’t kid yourself. When they say they don’t care about their lives, you have to take out their families,” Trump told Fox News in December.

Trump said he would “knock the hell out of” ISIS, and criticized the U.S. for “fighting a very politically correct war.”