The arrests this month in three U.S. cities of eight foreign nationals with suspected ties to terror group ISIS has further heightened concerns about a possible attack on American soil, officials are warning.
Since the arrests, Sen. Lindsey Graham (R-S.C.) has requested a classified briefing for all senators detailing ISIS threats against the U.S. in a letter tp Majority Leader Chuck Schumer (D-N.Y.) and Minority Leader Mitch McConnell (R-Ky.).
"I believe that the threat is urgent," Graham wrote.
One source told CNN: "ISIS isn't done with us."
Former acting CIA director Michael Morell starkly warned a day before news of the arrests in Foreign Affairs: "The United States faces a serious threat of a terrorist attack in the months ahead."
He wrote that "several serious plots in the United States" had already been foiled.
The immigrants from the former Soviet Republic of Tajikistan were arrested in Los Angeles, Pittsburgh and New York, and all currently face immigration charges, authorities confirmed to CBS News Tuesday.
They entered the country through the southern border last spring. There was nothing in routine screening that identified them with any links to a terror organization, a source told the Associated Press.
There is no known active terror plot the men are linked to, but they came to the attention of authorities through a wiretap in which one of them referred to a bombing, the New York Post was the first to report. He noted that something like the 2013 Boston Marathon bombing "might happen again or worse," according to the Post.
The Department of Homeland Security and the FBI said in a joint statement that agents of Immigration and Customs Enforcement had arrested the men in "close coordination with the FBI's Joint Terrorism Task Forces" over a number of days earlier this month.
The "individuals arrested are detained in ICE custody pending removal proceedings ... The FBI and DHS will continue working around the clock with our partners to identify, investigate, and disrupt potential threats to national security," the statement added.
The agencies noted that the U.S. has been in a "heightened threat environment."
