The admission, made at a House oversight hearing examining immigrant vetting in the wake of major terror attacks, drew a sharp rebuke from the committee chairman.
“You don’t have a clue do you?” Rep. Jason Chaffetz, R-Utah, told Michele Thoren Bond, assistant secretary for the Bureau of Consular Affairs.
Bond initially said the U.S. has revoked more than 122,000 visas since 2001, including 9,500 because of the threat of terrorism.
But Chaffetz quickly pried at that stat, pressing the witness about the present location of those individuals.
"I don't know," she said.
The startling admission came as members of the committee pressed administration officials on what safeguards are in place to reduce the risk from would-be extremists.
At issue is how closely the U.S. government examines the background of people seeking entry to the country, including reviews of their social media postings.
Leon Rodriguez, director of U.S. Citizenship and Immigration Services, told committee members that such checks aren't being done in an abundant manner, and he was not specific about when or how it would occur.
Lawmakers are trying to ascertain which safeguards are in place to ensure that extremists are not exploiting a variety of legal paths to travel to the United States.
One of the San Bernardino, Calif., shooters came to the U.S. on a K-1 fiancee visa last year despite the fact that the FBI believed she was already radicalized.
Tashfeen Malik came to the U.S. on a K-1 fiance visa in July 2014 and passed multiple background checks and at least two in-person interviews, one in Pakistan and another after she married Syed Farook. FBI Director James Comey has said Malik and Farook communicated privately online about jihad and martyrdom before they married.
Lawmakers at times angrily pressed officials on why even public social media wouldn't routinely be looked at for vetting those trying to enter the country.
"If half the employers are doing it in the United States of America, if colleges are doing it for students, why wouldn't Homeland Security do it?" said Rep. Stephen Lynch, D-Mass. "We don't even look at their public stuff, that's what kills me."