U.S. military forces have killed 60,000 Islamic State militants over the past two years, according to a U.S. Special Operations Commander.

On Tuesday, while speaking at a defense conference near Washington D.C., Army Gen. Raymond Thomas said the figure is substantially higher than the one reported at the end of last year – when U.S. officials said they had killed 50,000 ISIS fighters.

“I’m not into morbid body count, but that matters,” Thomas said at the National Defense Industrial Association’s annual Special Operations/Low Intensity Conflict conference, according to the Military.com. “So when folks ask, do you need more aggressive [measures], do you need better [rules of engagement], I would tell you that we’re being pretty darn prolific right now.”

But Defense Department Spokesman Christopher Sherwood told Fox News that death tolls are not a proper measure of “effectiveness” in the fight against ISIS.

“References to enemy killed are estimates, not precise figures,” Sherwood told Fox News via email. “While the number of enemy killed is one measure of military success, the [U.S. military] coalition does not use this as a measure of effectiveness in the campaign to defeat ISIS.”

Sherwood told Fox News that the Department of Defense measures the effectiveness of operations on the “impact” they have on the enemy’s ability to “hold territory and to plan, finance, and conduct terrorist operations.”

“It’s obviously encouraging that the United States has been able to identify and take that many people off of the battlefield,” Robin Simcox, the Margaret Thatcher Fellow focusing on terrorism and national security at Heritage Foundation, told Fox News. “But the fact that we’ve killed 60,000 fighters and there’s still so much more to be done – either they picked up their recruitment methods, or we underestimated the manpower they had on the ground.”

Simcox said ISIS continues to recruit terrorists willing to carry out attacks, which shows “we’ve barely made a scratch.”

He added that while the recent efforts to fight ISIS are impressive, he doesn’t see the Trump administration eliminating the terrorist group any time soon.

“Secretary Mattis is ideally placed to help fight this war, but as a society we need to accept the fact that this problem transcends any administration,” Simcox said. “This is an enormous ideological movement that has had various manifestations over the past decades, and it will outlive the Trump administration. ISIS is just the latest, most visible manifestation of this Islamic movement—[and] it has deep roots.”

While he said it would be difficult to dismantle ISIS, it’s not impossible.

“The only way to defeat this is to discredit the ideological component,” Simcox told Fox News. “That is the only way you’ll make any real headway.”