An increasing number of migrants arrested at the southern border over the past year are on the United States’ terrorist watch list, according to government data.
From October last year to this September, officials at the southern border arrested 169 people whose names matched those on the watch list, compared with 98 during the previous fiscal year and 15 in 2021, according to government data. But that is a minuscule fraction of the total number of migrants who were apprehended at the border over the past year, more than two million.
The increase appears to reflect at least two factors, a surge in illegal crossings and the number of people arriving from a wider variety of countries than in previous years.
Still, Republicans have seized on those numbers to assail President Biden for border policies that they say make Americans unsafe.
Representative Mark E. Green, Republican of Tennessee and chairman of the House committee on homeland security, pointed to the arrests on Wednesday during a hearing on global threats to the United States.
“Why would these individuals, who under the previous president, only 11 attempted to cross and were caught, suddenly feel like they could try and succeed?” he asked. (During the 2017-2019 fiscal years, under President Donald J. Trump, a total of 11 migrants on the watch list were arrested at the southern border.)
“And those are just the ones we know about,” Mr. Green added. The government estimates about 600,000 migrants crossed the southern border without detection.
Christopher A. Wray, the F.B.I. director, acknowledged that the increase in encounters with people associated with known or suspected terrorists was reason for concern. But in noting the uptick in a recent assessment, Homeland Security Department intelligence analysts said it did not reflect a growing terrorism threat.
Under the Biden administration, illegal border crossings have reached historic highs. A rising number of migrants are also arriving from more countries.
People from at least 230 countries have been arrested in the past year and face deportation in immigration court, according to data collected and analyzed by the Transactional Records Access Clearinghouse at Syracuse University.
In particular, the number of migrants from Colombia has increased sharply in the past two years. Some of those people may have had ties to the Revolutionary Armed Forces of Colombia, or FARC, once the country’s largest rebel group, according to an intelligence analyst who spoke on the condition of anonymity to discuss national security issues.
The United States removed the FARC from its list of foreign terrorist organizations nearly two years ago after a 2016 peace deal in Colombia’s decades-long conflict.
The terrorist watch list is a broad intelligence database containing more than one million names of known and suspected terrorists, as well as people with ties to them, including family members. When migrants are arrested after crossing the border illegally, officials run their names against the watch list and do other background checks.
“In most of these cases, it’s ultimately determined through further investigation that there is no connection with terrorism and that individual,” said John Cohen, a former counterterrorism adviser who once served as acting head of the intelligence and analysis division at the Homeland Security Department.
Customs and Border Protection publishes few details about the people whose names match those on the terrorist watch list or what then happens to them. Border officials coordinate with the F.B.I. on whether the person should be allowed to stay in the country or be removed.
The list has long been criticized for the opaque standards under which people’s names are added to it and for generating false matches. It can take years to remove the names of people associated with groups no longer considered to be a terrorist threat.
Often people are mistaken for someone on the watch list because they happen to have the same or a similar name.
The southern border has not been a route terrorists have taken to get to the United States in the past. No one has been killed or injured in a terrorist attack in the United States that involved someone who came across the border illegally since 1975, said Alex Nowrasteh, the vice president for economic and social policy studies at the Cato Institute, a libertarian think tank.
