NEW YORK CITY (NewsNation) — The U.S. remains in a heightened threat environment for both foreign and domestic terrorism following two arrests this week. The latest occurred Wednesday during a traffic stop in New York City. Officers found a cache of weapons in the man’s car, including knives, axes, a machete, a gun, ballistic vests and a mask. NYPD officials say they are investigating the suspect for possible terrorist ties.

In the past few days, eight people from Tajikistan with suspected ties to the Islamic State group were arrested in New York, Philadelphia and Los Angeles, the Department of Homeland Security confirmed to NewsNation.

The suspects entered the U.S. through the southern border, and are being held on immigration violations, said multiple people familiar with the matter who spoke to The Associated Press on condition of anonymity.

The nature of their suspected connections to the IS was not immediately clear, but the individuals were being tracked by the FBI’s Joint Terrorism Task Force, or JTTF, for months. They were in the custody of U.S. Immigration and Customs Enforcement, which made the arrests while working with the JTTF, pending proceedings to remove them from the country.

Crossing the border

The individuals from Tajikistan entered the country last spring and passed through the U.S. government’s screening process without turning up information that would have identified them as potential terrorism-related concerns, said one of the people familiar with the matter.

A joint statement from the FBI and DHS confirmed the arrests:

“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 FBI and DHS will continue working around the clock with our partners to identify, investigate, and disrupt potential threats to national security.”

Sources familiar with the operation said the individuals had been vetted by law enforcement upon entering the U.S., and there was no indication that they had ties to ISIS at the time.

However, law enforcement subsequently became concerned with their presence in the States and took action, officials said.

Increased national security threat: Wray

The arrests came months after FBI Director Christopher Wray warned of an increased national security threat. He testified before Congress in April about concerns that human smuggling operations at the border were bringing in people with possible connections to terror groups.

“I will tell you that we have any number of instances where somebody who is of concern, where there wasn’t adequate biometrics or other identification information at the time they came across, then later information is found that highlights why they’re of concern. And then it’s the FBI and our partners who have to then go try to find the person, take whatever action we can to disrupt the threat that that person poses,” Wray testified.

Wray also warned of a possible coordinated attack in the U.S. following the ISIS-K terror attack in March on a Russian concert hall where 145 people were killed.

“The FBI and DHS will continue working around the clock with our partners to identify, investigate, and disrupt potential threats to national security,” the agencies said.

The Associated Press contributed to this report.