Law enforcement authorities in Washington, D.C., are worried that members, supporters and lone wolves linked to the Islamic State have the nation's capital high on the attack list.

"When we look at the threat reporting emanating from ISIL and other [homegrown violent extremists] around the country, we know there is a constant and persistent threat to the district," Joshua Skule, who was special agent in charge of intelligence at the Washington Field Office of the FBI at the time, told WTOP earlier this month.

Skule, who is now assistant director for intelligence, said he believes the threat is real, and that the Islamic State has recruited people in D.C. and the surrounding region to work on its behalf.

"They are prolific on the web. Their propaganda message on social media has been consistent and it has resonated, as our director [James Comey] has said, with lost souls looking for a place to go," Skule said. "Their foreign fighter flow into that region is something we, the world, has never seen to the volume that the world has seen today."

According to intelligence sources, it's not just the aggressive online recruiting done by the terror organization, but rather the group's systematic deterioration abroad that has given recruits a reason to escape the organization and flee to the United States.

In addition, airstrikes and ground assaults have forced Islamic State fighters not simply to hide in locations in Syria and Iraq, but also give up the on-the-ground fight and return to either their home countries or others to carry out violence.

"There's always concern about foreign fighters coming back to the U.S., specifically to D.C., to do harm," Skule said.

Islamic State fighters have also been forced to accept a pay cut, which has led to departures. However, Skule still says "ISIL is the most prolific threat we have faced ... Their call to jihad and their message to kill at every turn is something we have never undertaken or faced, even with core al Qaeda. It would give a terrorist organization no greater benefit than to attack the seat of power in the U.S."