Threat of American ISIS Fighters 'Not Even Close to Being Under Control,' Top FBI Official Says

— -- The head of the FBI’s counterterrorism division was blunt about the threat here at home from Americans who’ve trained with terrorist groups like ISIS overseas: “We don’t have it under control.”

“It’s not even close to being under control,” FBI Deputy Assistant Director Michael Steinbach told House members today.

Over nearly three hours of testimony before the House Homeland Security Committee, Steinbach laid out the evolving threats facing the U.S. homeland and the efforts underway to stop them. He was joined by the director of the National Counterterrorism Center and the Department of Homeland Security’s top intelligence official.

All three agreed that because of few intelligence assets on the ground in the region, particularly in Syria, the U.S. government has little insight into who’s joining terrorist groups there, and who’s then leaving with what NCTC director Nicholas Rasmussen described as “training in weapons and explosives” and “access to terror networks that may be ultimately planning attacks” against the West.

“In many cases the information we have on foreign fighters traveling to the conflict zone stops when they get there,” Rasmussen warned.

Within its ranks, ISIS is estimated to have 50,000 “barbarians,” as the committee’s chairman, Rep. Michael McCaul, R-Texas, put it. In Syria and Iraq, fighting with ISIS and other groups, there are more than 20,000 foreign fighters, including at least 3,400 recruited from Western countries, the U.S. officials said today.

“It exceeds the rate of travelers who went to Afghanistan and Pakistan, Iraq, Yemen, or Somalia or other prominent conflict zones ... at any point in the last 20 years," Rasmussen said.

Of the dozens of Americans who have gone to Syria or Iraq and trained with terrorists there, “a small group” of them have returned to the United States and are now being tracked by the FBI, sources previously told ABC News.

But today, Steinbach told lawmakers: "It would not be true if I told you that we knew about all of the returnees. … We know what we know.”

Nevertheless, authorities are “doing the best we can” to keep tabs on Americans and others traveling to Syria or Iraq, and to develop new “processes” to identify travelers, Steinbach said. He suggested automated searches of social media could help deal with the problem.

Steinbach described ISIS’ online efforts as “dangerously competent like no other group before,” using social media and other Internet forums “to both radicalize and recruit.”

Since the beginning of last month alone, ISIS has published more than 250 “official products” online, and those postings “reach wide and far almost instantaneously, with reposting and regeneration of follow-on links” in “an ever-growing number” of languages, according to Rasmussen.

Such a proliferation has spawned a new “blended threat,” bringing “foreign-fighter ideology” to homegrown extremists who have no real connection to terrorist groups overseas and are difficult to detect, Steinbach said.

“With the widespread horizontal distribution of social media, terrorists can identify sympathetic individuals of all ages in the United States – spot, assess, recruit, and radicalize either to travel or conduct a homeland attack,” Steinbach said. "A foreign terrorist now has direct access into the United States like never before."

Indeed, U.S. officials believe there are “a few hundred individuals” inside the United States who could be inclined to launch their own attacks, and the public should expect several – but fewer than 10 – “uncoordinated and unsophisticated plots” each year, Rasmussen said in a written statement submitted to the House committee before his testimony.

The head of Intelligence and Analysis at DHS, Under Secretary Francis Taylor, said such threats underscore the need for "increased vigilance" across government and in public.

Fighting online recruitment and radicalization efforts is difficult and complicated, the U.S. officials noted. While the U.S. government has “direct engagement” with the big companies such as Twitter, Facebook and YouTube, a “large number” of social media sites are hosted overseas by companies “who flaunt their lack of cooperation with law enforcement,” according to Steinbach.

Still, Steinbach said he has a “grave concern” over new phones and other devices being developed by the major tech companies, devices that allegedly leave no ability for authorities to collect information, even when a court approves it. The FBI has dubbed the growing issue “Going Dark.”

“This real and growing gap … must be urgently addressed because the risks of going Dark are great,” Steinbach, adding, "Without that lawful tool, we risk an attack."