WASHINGTON — The secretary of homeland security said Wednesday that the United States has tracked down the majority of about 6,000 unaccounted-for foreign students who had overstayed visas and spurred concerns over Islamic State-linked terror attacks.

Most have either been deported or had visas extended while a fraction remain under investigation, Secretary Jeh Johnson said during testimony to the House Homeland Security Committee.

Top national security officials including Johnson, FBI Director James Comey and National Counterterrorism Center Director Matthew Olsen told House lawmakers that they have still not discovered any specific Islamic State plans to strike targets inside the U.S., but that monitoring a burgeoning worldwide network of extremists remains a challenge.

News earlier this month that about 6,000 foreign students studying in the U.S. had disappeared raised fears at a time when the Obama administration is vastly expanding its military and diplomatic offensive against the Islamic State in Iraq and Syria.

“There is a fraction of that population where there is still open investigations,” Johnson said, though he did not specify exactly how many cases are unresolved.

Comey said security agencies are also working to track potential extremists who come and go from the U.S., possibility being trained or helped Islamic State forces in the Middle East.

“There is thousands of ways to get from the United States to Syria … I’m not overly confident, given the nature of the challenge,” he said.

House lawmakers hammered the officials over the security of the country’s southern border, where thousands of undocumented immigrants, many of whom are children, have been flowing in.

Rep. Lou Barletta, R-Pa., said that closing the border should be a key goal in fending off terrorist attacks even if officials have no specific evidence of plans or extremist movements.

“That is not a good reason — that we should not secure the border because we believe nobody has crossed over the border,” he said.

Twitter: @Travis_Tritten

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