WASHINGTON — With no regular American presence in the war theater, the U.S. has struggled to answer basic intelligence questions about the situation in Syria and Iraq, including the Islamic State group’s fighting strength. And the overall U.S.-led bombing campaign has failed to dislodge the group from its self-declared caliphate across both countries.

But one element is seen as a growing intelligence and military success: The combined effort by the CIA and the military’s Joint Special Operations Command to find and kill “high value” targets from both al-Qaida and IS.

The drone strikes — separate from the large air campaign run by U.S. Central Command — have significantly diminished the threat from the Khorasan Group, an al-Qaida cell in Syria that had planned attacks on American aviation, officials say. The group’s leader, Muhsin al-Fadhli, and its top bomb-maker, David Drugeon, were killed this summer. Other targeted strikes have taken out senior Islamic State group figures, including its second in command, known as Hajji Mutazz.

In an effort that ramped up over the last year, intelligence analysts and special operators have harnessed an array of satellites, sensors, drones and other technology to find and kill elusive militants across a vast, rugged area of Syria and Iraq, despite the lack of a ground presence and steps taken by U.S. targets to disguise their use of electronic devices.

The strikes won’t defeat the Islamic State, but they are keeping its leadership off balance, a senior defense official involved in planning them said. “They are constantly having to adjust, which means they don’t have a lot of time to sit there and plan large and effective attacks,” the official said.