(CNN) The United States is maintaining a list of about two dozen or so top ISIS operatives in Iraq and Syria that it hopes to target in airstrikes, according to a senior U.S. official.
The list essentially amounts to a kill list, since the United States has no troops on the ground in Iraq or Syria to capture ISIS suspects. The No. 1 target on the list is Abu Bakr al-Baghdadi, the leader of ISIS.
One U.S. official said al-Baghdadi is well-aware the United States is hunting him, so the belief is he is staying out of sight.
It's been months since the last intelligence report about where al-Baghdadi is hiding, a senior U.S. official tells CNN.
The United States believes al-Baghdadi knows warplanes are hunting him, so he moves cautiously -- even as his influence has grown beyond Syria and Iraq.
The United States has already killed a dozen or so ISIS operatives on the list, including an ISIS chemical weapons expert, the senior official says. But others are added to the list as intelligence is gained about their role in ISIS.
The official strongly emphasized that the command-and-control structure of ISIS remains murky and more intelligence is needed about the identity of top operatives.
ISIS executioners such as so-called Jihadi John are still in the U.S. crosshairs -- but the list focuses on targeting those whose death would broadly hurt ISIS. The kill list may now expand as the United States struggles to understand an ISIS command structure made more confusing by the growth of ISIS adherents in Egypt, Yemen, Afghanistan, Pakistan and Libya.
One analyst cautions those labeling themselves as ISIS might have very different goals.
"We have to take each terrorist or cult organization in every country as a separate entity. We can't look at it as one big group. You may miss the most important targets when you are doing that," said Mark Hertling, CNN military analyst.
The growing -- and alarming -- reach of ISIS
The execution of Egyptian Christians on the Libyan coastline underscores the targeting problem. The United States wants to identify the killers. But the broader worry is ISIS' position in Libya. It now has a stronghold in Derna and operates across Libyan coastal areas within reach of southern Europe via busy shipping lanes.
"It's very difficult to have the same kind of controls over people who might be getting on boats who might be working as stevedores or laborers on ships that are coming into European ports," Hertling said.