Over 1,000 Israelis were killed by Hamas terrorists who stormed across the country’s southern border over the weekend. And one immigration expert told Fox News Digital it’s a reminder the U.S. southern border is vulnerable to terrorist crossings. 

“Absolutely,” Lora Ries, director of the Border Security and Immigration Center at The Heritage Foundation, told Fox News Digital this week when asked if the Hamas attack on Israel serves as a warning that the southern border with Mexico is not secure and is vulnerable to national security threats.

“Particularly the 1.7 million known ‘gotaways,’ those who evaded the Border Patrol because they didn’t want to be fingerprinted because they’re either known or suspected terrorists themselves, convicted aggravated felons, smuggling drugs or some combination thereof. 

“So, when you combine 1.7 million with the 7.4 million CBP has encountered, we have to assume that the sleeper cells of terrorists are here inside the U.S., and Congress needs to wake up and preempt.”

BIDEN ADMIN MAY HAVE LOST TRACK OF MILLIONS OF MIGRANTS CROSSING SOUTHERN BORDER: CONGRESSIONAL REPORT

Ries, who has over 26 years experience in the immigration and homeland security field and served as DHS acting deputy chief of staff, told Fox News Digital she is concerned about sleeper cells in the U.S. “waking up.”

“And already with the Hamas, pro-Hamas protests in the U.S. this week in New York City and elsewhere. That was a very public signal to say, ‘Yes, we’re here.’ And if the U.S. acts to support Israel in the Middle East then there will be a response here,” Ries said. 

“They don’t need to fly in on their Mad Max devices like they did this past weekend in Israel,” Ries added. “They’re already here.”

DEMOCRATS SUPPORT PALESTINIANS OVER ISRAEL; GOP OVERWHELMINGLY STANDS WITH US ALLY: 2023 POLL

Asked about national security threats in the United States after Hamas’ attack on Israel, a spokesperson at the Department of Homeland Security (DHS) told Fox News Digital Wednesday DHS does “not have specific and credible intelligence indicating a threat to the United States at this time stemming from the Hamas terrorist attacks in Israel.”

The DHS spokesperson added the department is “closely monitoring unfolding events and will continue to engage in information sharing with our intelligence and law enforcement partners at home and abroad.”

Thousands of “special interest aliens” from various countries and regions, including the Middle East, have been arrested by Border Patrol agents attempting to cross the U.S. southern border illegally over the last two years, internal Customs and Border Protection (CBP) data leaked to Fox News shows.

Special interest aliens are people from countries identified by the U.S. government as having conditions that promote or protect terrorism or potentially pose some sort of national security threat to the U.S. 

ISRAELI MUSIC FESTIVAL SURVIVOR DESCRIBES HORROR OF HAMAS-LED ATTACK THAT LEFT 260 DEAD

For over two years, Border Patrol agents have warned that they have extreme concerns about who is crossing the southern border, primarily because so many agents have been pulled off the front lines to instead focus on processing, leaving gaps where there is no control over the border, Fox News national correspondent Bill Melugin reported Tuesday.

Meanwhile, fiscal year 2023 broke the record for encounters on the FBI terror watchlist, with 151 people encountered at the southern border between ports of entry, a higher number than the previous six years combined.

Ries told Fox News Digital that DHS Secretary Alejandro Mayorkas has been asked “numerous times” about the current location and status of the 151 individuals who crossed the border while on the terror watch list, and he has “refused to answer.”

“Americans have no confidence in this administration, and we do not and should not get to the point where a terrorist attack is committed here. And then members of Congress look at each other and ask, ‘How did this happen? How did we get here?’” Ries said.

“This information sharing helps ensure that we are positioned to help mitigate any risks to national security or public safety,” a DHS spokesperson said in a statement to Fox News Digital. “Our multilayered border security efforts include various screening and vetting processes that work to detect and prevent individuals who pose national security or public safety risks from entering the United States.”

The department added that it is “prepared to respond to any potential impacts to public safety, and the “United States will not hesitate to adjust our security posture, as appropriate, to protect the homeland and the people of the United States.”

Fox News Digital’s Adam Shaw and Bill Melugin contributed to this report