The U.S. Central Intelligence Agency (CIA) and Joint Special Operations Command (JSOC) forces have begun hunting terrorism suspects with drones in Syria, in a secret program that operates independently of the larger U.S. military offensive against the Islamic State group in the region, according to media reports.

The CIA and JSOC’s collaborative efforts have been responsible for the deaths of several senior ISIS operatives in recent months, according to unnamed U.S. officials cited by the Washington Post. Among those killed was Junaid Hussain, a British fighter who was thought to be a major part of the group’s social media program to incite attacks in the United States.

The clandestine program has also seen the CIA enlist its Counterterrorism Center (CTC) against ISIS, a threat that several U.S. officials warn has surpassed al Qaeda as the primary threat from global Islamic extremism, the Washington Post reported.

The CTC has been given an enhanced role in identifying and locating senior ISIS figures, but officials reportedly said that the strikes are being carried out exclusively by JSOC, and only against individuals identified as “high-value targets.”

A senior U.S. official said that the targets “are being identified and targeted through a separate effort,” according to the Washington Post.

The decision comes after President Barack Obama's decision to shift the power to conduct drone strikes from the CIA to the Pentagon earlier this year. He announced the decision in April after the White House admitted that two Western hostages were killed in a CIA-led drone strike on militants.

That incident led Obama and other lawmakers to push for control to be taken away from the CIA and placed back in the hands of conventional military command.

But leaders of the Senate Intelligence Committee reportedly sent a classified letter warning against any attempt to weaken the CIA’s anti-terrorist activities. Several senior lawmakers also disputed Obama’s efforts.

However, officials reportedly said that the new CIA program reflects a growing frustration and anxiety about the potential ISIS has to destabilize the entire region, and its stubborn resistance to conventional attacks.

To that end, the CTC, which pioneered the use of drone strikes in Afghanistan in the early 2000s and led the search for former al Qaeda leader Osama bin Laden, and JSOC, which was responsible for the commando raid that killed him, have begun coordinating on strikes.

However, officials said that their program has been responsible only for a tiny portion of the over 2,450 drone strikes in Syria so far. The U.S.-led coalition against ISIS has also conducted over 4,000 other strikes, where it has relied on aerial bombing.