The United States suffers from an intelligence "gap" on the ground in Syria, which has stymied the government's ability to track Western foreign fighters, including Americans, fighting there with ISIS and al Qaeda's affiliate, senior U.S. counter-terrorism officials told lawmakers today.

"It is a tremendously challenging collection environment for all of our intelligence agencies because we are not present on the ground there in the traditional way. We don't have the footprint on the ground there the way we would in many places around the world with a diplomatic, military, intelligence presence," Nicholas Rasmussen, director of the National Counterterrorism Center, testified at a House hearing.

"And so we are forced to be more creative, more innovative, more entrepreneurial in trying to close that gap," he told the House Committee on Homeland Security in a hearing on the threat posed by foreign fighters.

Intelligence officials have long whispered frustration over their inability to mobilize spies on the ground in the war-torn nation, where al Qaeda and ISIS battle each other as much as they fight the Syrian regime of Bashar al-Assad, and where they have kidnapped, tortured and murdered American and other western hostages.



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But rarely have U.S. officials admitted publicly just how hamstrung they are collecting intelligence inside Syria about U.S. enemies, where spy agencies must rely on airborne collection platforms such as drones and satellites to monitor communications, track terrorist leaders and take on the difficult task of finding hostages' locations.

Tuesday the White House announced the confirmed death of the last known American hostage in ISIS hands, Kayla Jean Mueller, 26, of Prescott, Ariz. Americans James Foley, Steven Sotloff and Peter Kassig were beheaded by ISIS in gruesome videos since August. British, Jordanian and Japanese captives have also died horribly in the hands of the terror group.

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All were held together in various Syrian locations since 2013, including in an old oil refinery near the ISIS stronghold Raqqa, where special operators from the Army’s Delta Force attempted a rescue operation on July 3. President Obama told BuzzFeed Tuesday that the team "probably missed them by a day or two."

Officials have told ABC News that the dearth of ground intelligence contributed to the failure of the operation and the difficulty of other hostage rescue attempts since.

Despite efforts to improve collection -- which counter-terrorism officials have told ABC News has never included presidentially-authorized human intelligence on the ground in Syria -- the U.S. has a long way to go, officials told lawmakers.

"I would not argue though that we have closed the gap on where we need to be in terms of our understanding, with granularity, about what is going on on the ground in Syria. In many cases the information we have about foreign fighters traveling to the conflict zone stops when they get there," Rasmussen admitted.

His remarks echoed a similar admission last year by his NCTC predecessor, Matthew Olsen, now an ABC News contributor.

One of the worst -- yet little-discussed publicly -- failures in tracking American foreign fighters was a Florida man, Moner Muhammad Abu Salha, who traveled to Syria and back to the U.S. before returning to Syria a second time last year to carry out a suicide truck bombing of an Assad regime military outpost.

"This individual, who later committed a suicide attack in Syria, did return to the United States from Syria without our knowledge and I think without -- was not under FBI investigation. It was only after his suicide attack that we learned of his activity. I think that incident really reinforced our understanding of the need to have better intelligence about what was going on in Syria," testified Francis Taylor, the undersecretary for intelligence and analysis at the Department of Homeland Security.

"How did we miss him? What has changed?" Rep. Scott Perry (R-Penn.) demanded.

Taylor replied that information sharing with European agencies has improved, but he did not explain how Abu Salha evaded detection and became only a handful of Americans to have ever perpetrated a suicide bombing.