Five Syrian men were arrested by Border Patrol agents as they crossed into Hidalgo, Texas, on Thursday, a Department of Homeland Security (DHS) source told Fox News.

The men were picked up by Rio Grande Valley sector agents and mark one of a number of nationalities picked by Border Patrol, many of them from countries far away from the land borders of the United States.

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There were more than 178,840 migrant apprehensions in December, after a year that saw monthly apprehensions at over 212,000 at one point during the surge. Border Patrol agents have been overwhelmed by the numbers, while it has caused a political headache for the Biden administration -- which has been accused of fueling the crisis by ending key Trump-era border policies.

The number of migrants coming north, as well as high estimates of the numbers who have slipped past border agents, has raised concerns that terrorists and other criminals will try to get into the U.S.

Raul Ortiz, deputy chief of U.S. Border Patrol, speaks during a new conference in Brownsville, Texas, U.S., on Thursday, Aug. 12, 2021.  Mexico Foreign Minister Marcelo Ebrard and a high level delegation of government officials advanced talks with U.S. officials, including Homeland Security Secretary Mayorkas, on on topics of migration, border security and economic development. Photographer: Veronica G. Cardenas/Bloomberg via Getty Images

Raul Ortiz, deputy chief of U.S. Border Patrol, speaks during a new conference in Brownsville, Texas, U.S., on Thursday, Aug. 12, 2021.  Mexico Foreign Minister Marcelo Ebrard and a high level delegation of government officials advanced talks with U.S. officials, including Homeland Security Secretary Mayorkas, on on topics of migration, border security and economic development. Photographer: Veronica G. Cardenas/Bloomberg via Getty Images

There were 10,763 arrests of migrants with criminal convictions in FY 2021, up from 2,438 in FY 2020 and 4,269 in FY 2019. Meanwhile, Republicans have been pushing for DHS to publicly reveal how many known or suspected terrorists have been encountered at the border.

Former Border Patrol Chief Rodney Scott has repeatedly sounded the alarm over the number of individuals in the Terrorist Screening Database coming across the border, telling fellow agents that it was "at a level we have never seen before. "

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Syria has been designated a state sponsor of terrorism and was one of the seven countries on the initial Trump-era travel ban in 2017 due to the perceived national security threat. There was no immediate indication any of the five men arrested Thursday had any terror ties.

Former acting Immigration and Customs Enforcement (ICE) Director Thomas Homan told Fox News on Saturday that "when you have an uncontrolled border, when you have massive illegal immigration that takes half the Border Patrol offline, bad people will come across the border where the Border Patrol is tied up."

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"Border Patrol has arrested 16 on the FBI screening database, there’s half a million gotaways…How many of those 500,000 could be known or suspected terrorists?" he asked. "Now they’re arresting people from Syria -- this is a national security crisis that Joe Biden created."