"I would give us a 5, which means we have a lot of work to do," Lt. Gen. Robert "Bob" Otto told CNN on Friday, when asked to evaluate the air targeting on a 10-point scale.
"We are the best in the world at what we do. But there is always room to improve," he said.
Other Air Force officials tell CNN they believe a number of targeting improvements have been made.
CIA Director John Brennan acknowledged Wednesday that the United States had room for improvement when it came to taking on ISIS, also known as ISIL or Daesh.
The U.S. still has "a ways to go before we are able to say we have made some significant progress against" ISIS, Brennan said at an event at the Council of Foreign Relations.
Brennan said that Tuesday's terror attack on Istanbul's Ataturk Airport "certainly bears the hallmarks of ISIL's depravity."
Turkish Prime Minister Binali Yildirim said Tuesday that "The signs point to Daesh, but investigation is ongoing."
Brennan said that it was "not surprising" that ISIS had not yet claimed responsibility, noting that ISIS typically did not claim responsibility for attacks in Turkey because the terror group hoped to still attract sympathizers there.
Brennan and other officials have said that ISIS's recent spate of battlefield losses might drive ISIS to strike targets outside its territory.
"To compensate for territorial losses, ISIS will probably rely more on guerrilla tactics, including high profile attacks outside the territory in Syria and Iraq that it currently holds," Brennan told the Senate Intelligence Committee earlier this month.
State Department spokesman Mark Toner made a similar linkage while briefing reporters.
"They're under pressure. But that does not affect their ability to carry out terrorist attacks either in Europe or elsewhere in the world," Toner said.
"They are still capable, and in their desperation, even perhaps more willing and liable to carry out these kind of attacks," he said.
But the spokesman for the anti-ISIS coalition, Col. Christopher Garver, briefing reporters on Tuesday, presented a rosier perspective.
He said that the air campaign was having a major impact on the terrorist group's ability to recruit new fighters.
"What are we doing to stop recruitment? I think the No. 1 thing is through B-52s and through A-10s and through F-16s, and Mirages and the other aircraft that are conducting strikes," he said.
"The more we can kill, the more we can destroy Daesh on the ground," he continued. "I think we're doing a good job of convincing people that, you know, being a recruit, being a leader, there's not a lot of long-term career options in Daesh."
But Brennan expressed caution.
"Right now I am still very concerned that the ISIS-generated engine of foreign terrorism outside of Syria and Iraq still has a lot of momentum."
He concluded, "We cannot rest at all. We have to increase our efforts", CNN reported.
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