FBI Director Christopher Wray told senators on Monday that there are “very dangerous threats” coming from the U.S.-Mexico border, including a smuggling network with “ISIS ties.”

Sen. Marco Rubio, R-Fla., asked Wray during a Senate Intelligence Committee hearing Monday regarding threats at the southern border, Fox News reported.

“I want to be a little bit careful how far I can go in open session, but there is a particular network that, where some of the overseas facilitators of the smuggling network have ISIS ties that we’re very concerned about and that we’ve been spending enormous amount of effort with our partners investigating. Exactly what that network is up to is something that’s, again, the subject of our current investigation,”