TONIGHT: A Must-See 'War Stories' Goes Deep Inside the ISIS Threat

U.S. special ops forces have killed the #2 leader of ISIS in a pre-dawn raid Thursday in Syria, senior defense officials confirmed to Fox News.

Iraqi Abd al-Rahman Mustafa al-Qaduli, also known as Abu Ala al-Afri, had a $7 million bounty on his head from the U.S. and was considered the top deputy of ISIS leader Abu Bakr al-Baghdadi.

Al-Qaduli joined ISIS after being released from prison in early 2012 and traveled to Syria. He served under the command of Abu Musab al-Zarqawi, the now-deceased leader of al Qaeda in Iraq.

Defense Secretary Ash Carter also announced the killing of another senior ISIS leader, nicknamed "Omar the Chechen." Referred to as the terror army's "minister of war," Omar al-Shishani was killed in a recent US airstrike.

Fox News Pentagon correspondent Jennifer Griffin reported that al-Qaduli is a former physics professor, describing the killing as a "big get."

Carter acknowledged that these figures will be replaced, but said they are "senior and experienced" leaders in the organization. 

"It's necessary [to take out ISIS leaders] but it's not sufficient," Carter said.

Tune in tonight at 10:00pm ET for a must-see investigation of the ISIS threat on "War Stories: Fighting ISIS," which will feature an interview with Joint Chiefs Chairman Gen. Joseph Dunford.

Are America's Nuclear Plants Safe from a Terror Attack?

Siblings Who Lived in NY Confirmed Killed in Brussels Terror Attacks

'Who Is Advising Him?': Greta Blasts Obama's 'Tone Deaf' Tango