The FBI is investigating more than a dozen Uzbek nationals 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.