Updated

Eight Tajikistan nationals with ties to ISIS were busted by U.S. Immigration and Customs Enforcement (ICE) in conjunction with the Federal Bureau of Investigation’s (FBI) Joint Terrorism Task Force in three major cities, a federal source confirmed to Fox News.

The arrests took place in New York City, Los Angeles and Philadelphia in recent days, according to the source. 

All eight Tajikistan nationals crossed the U.S. southern border illegally, and according to a federal source familiar with the sting, no derogatory information was initially flagged with U.S. Customs and Border Protection (CBP) or with the U.S. Department of Homeland Security (DHS) during processing.

The suspected terrorists were "fully vetted" and nothing was flagged, according to Fox News' federal source. 

1M ILLEGAL IMMIGRANTS COULD BE GIVEN 'AMNESTY' AS BIDEN FACES PRESSURE FROM LEFT WING

ICE agents immigration

FILE- Eight Tajikistan nationals with ties to ISIS were busted by ICE and the FBI in New York City, Los Angeles and Philadelphia, a federal source confirmed to Fox News. (Immigration and Customs Enforcement)

Fox News’ source said after the suspected terrorists were released into the U.S., derogatory information was flagged with national security concerns, including the individual’s ties to ISIS.

The sting operation was first reported by the New York Post’s Jennie Taer. 

According to Taer's report, part of the investigation featured a wiretap which revealed one of the now-arrested individuals was talking about bombs.

"Remember the Boston marathon [bombing]? I’m afraid something like that might happen again or worse," one of the sources told The Post.

GOV. GREG ABBOTT SAYS BIDEN EXECUTIVE ORDER MAKING ILLEGAL BORDER CROSSINGS 'WORSE': 'GASLIGHTING' AMERICANS

When contacted about the report by Fox News, the FBI and DHS sent a joint statement:

"Over the last few days, ICE agents arrested several non-citizens pursuant to immigration authorities. The actions were carried out in close coordination with the FBI’s Joint Terrorism Task Forces. The individuals arrested are detained in ICE custody pending removal proceedings.  As the FBI and DHS have recently described in public and partner bulletins, the U.S. has been in a heightened threat environment. The FBI and DHS will continue working around the clock with our partners to identify, investigate, and disrupt potential threats to national security," - DHS/FBI joint statement

This all comes as FBI Director Christopher Wray told a Senate Appropriations subcommittee last week that there is an increasing concern of a potential coordinated attack in the U.S., similar to the Islamic State in Khorasan Province (ISIS-K) attack in March at a concert hall in Russia.

Wray told members of the subcommittee that when he met with them last year, he walked them through how the U.S. was already in a heightened threat environment, and since then, threats from foreign terrorists have risen to another level.

FBI DIRECTOR WARNS OF JIHADIST ATTACK IN US, SIMILAR TO RUSSIAN CONCERT HALL: 'HEIGHTENED TERRORIST THREAT'

FBI Director Christopher Wray speaking to a Senate Appropriations subcommittee

FBI Director Christopher Wray met with a Senate subcommittee on Tuesday, and warned of increasing concerns over a coordinated attack on U.S. soil, similar to the ISIS-K attack in Russia in March.

"Just in the time that I’ve been FBI director, we’ve disrupted multiple terrorist attacks and cities and communities around the country. We need funding to continue protecting America from terrorism," Wray previously said.

Wray warned the subcommittee that if Congress cuts their budget, it will have "very significant" consequences as the FBI would not be able to fill nearly 1,000 positions, meaning efforts to protect Americans from terrorism would fall short.

"That’s fewer tips and leads followed; fewer terrorist attacks detected. That’s a significant concern in a heightened terrorist threat environment," Wray said. "It helps out the terrorists, the cartels, the violent gangs, the Chinese government, the hackers, the child predators. I can go on and on."

CLICK HERE TO GET THE FOX NEWS APP

Wray was asked how the FBI prioritizes its resources to be able to protect communities from the various threats, and he pinpointed one major concern that drives all prioritization.

"Terrorism, which includes both foreign terrorism and domestic terrorism, remains our number one priority," Wray said.

Fox News Digital's Greg Wehner contributed to this report.