The FBI is investigating more than a dozen migrants from Uzbekistan and other countries allowed into the US after they sought asylum at the southern border with Mexico earlier this year, a scramble set off when US intelligence officials found that the migrants traveled with the help of a smuggler with ties to ISIS, according to multiple US officials.

While the FBI says no specific ISIS plot has been identified, officials are still working to “identify and assess” all of the individuals who gained entry to the United States, according to a statement from National Security Council spokesman Adrienne Watson. And they are closely scrutinizing a number of the migrants as possible criminal threats, according to two US officials.

Though there is no evidence at this point to justify detaining anyone, the episode was so alarming that an urgent classified intelligence report was circulated to President Joe Biden’s top Cabinet officials in their morning briefing book. For some counterterrorism officials, it shows that the US is deeply vulnerable to the possibility that terrorists could sneak across the southern border by hiding amid the surge of migrants entering the country in search of asylum.

The incident kicked off a flurry of urgent meetings among top national security and administration officials at a time when Republicans have hammered Biden on the security of the southern border heading into the 2024 campaign. Staff on key congressional committees have been informed of the incident, according to two sources familiar with the matter.

Earlier this year, a cohort of migrants from Uzbekistan requested asylum and were screened by the Department of Homeland Security, part of a rising number of asylum seekers who have traveled to the US from Central Asia in recent years. There was no information in any of the intelligence community’s databases that raised any red flags and the people were all released into the US pending a court date. 

It was only later, when the FBI learned about the existence of a human smuggling network helping foreign nationals travel to the US – and that this network included at least one individual with connections to ISIS – that national security officials put the pieces together.

FBI agents around the country immediately rushed to try to locate the migrants and investigate their backgrounds. The bureau also worked with Turkish authorities, who arrested the smuggler and other members of his network at the behest of the US, and has subsequently obtained information from him to aid its investigation, US officials said. 

“There was no indication—and remains no indication—that any of the individuals facilitated by this network have a connection to a foreign terrorist organization or are engaged in plotting a terrorist attack in the United States,” Watson said in a statement to CNN.

Since the intelligence became available, homeland security officials also began detaining, vetting and, ultimately, expediting the removal of other migrants encountered at the southern border who “fit the profile associated with individuals who were facilitated by this network,” Watson said.

The ISIS-linked smuggler is not believed to be a member of the terror group, but more like an independent contractor who has personal sympathies with the organization, according to US officials. The intelligence community now believes it is unlikely that he was assisting these individuals at the behest of ISIS. Most are believed to be seeking a better life in the United States.