Story highlights U.S. airstrikes have killed three high-level ISIS leaders

The killings had been suspected but finally confirmed on Thursday

U.S. airstrikes have killed two top-level and one mid-level ISIS leader, a senior U.S. military official tells CNN.

Haji Mutazz was Abu Bakr al-Baghdadi's deputy in Iraq; Abd al Basit was his military emir in Iraq; and Radwan Talib was his Mosul emir. Their deaths resulted from multiple strikes going back to mid-November -- it has taken until now to determine conclusively they were killed.

"I can confirm that since mid-November, targeted coalition airstrikes successfully killed multiple senior and mid-level leaders within the Islamic State of Iraq and the Levant," said Pentagon press secretary Rear Adm. John Kirby, in a statement on Thursday.

"We believe that the loss of these key leaders degrades ISIL's ability to command and control current operations against Iraqi Security Forces, including Kurdish and other local forces in Iraq," he said.

News of the killings was first disclosed by Joint Chiefs Chairman Martin Dempsey in an interview with the Wall Street Journal.

In addition, President Barack Obama signed deployment orders yesterday for 1,300 troops to Iraq. This is the lion's share of the 1,500 additional troops he authorized last month. By February, the U.S. will have roughly 3,000 U.S. troops on the ground.

The U.S. troops are also going further afield than they previously were: There are now nearly 300 U.S. forces at Al Asad base in Anbar province, up from just 50 earlier this month. The U.S. military is following through on announced plans to deploy these military advisers and trainers outside of Baghdad and Erbil.​