A surge in online militant activity is fueling concerns of imminent violence amid reports of ISIS ties to the Sydney shooting.

The do-it-yourself model was professionalized and has been really deployed around the world by ISIS, inspiring dozens of people to carry out attacks in their name,” one expert tells NBC News.

U.S. forces on Friday struck several ISIS targets in Syria after President Trump vowed revenge for the killing of two Iowa National Guard soldiers.

Last Saturday, an Islamic State infiltrator ambushed a meeting between American soldiers and their local counterparts in a Syrian desert town. Two members of the Iowa National Guard and a U.S. civilian interpreter were killed in the assault—whose perpetrator may or may not have known that the subject of the meeting was how to counter ISIS.

The police found two homemade Islamic State flags in the car of the suspects, a 50-year-old man and his 24-year-old son.

Deadly Syria attack kills two U.S. service members, intensifying pressure on Trump to reassess counter-ISIS strategy and partnership with Ahmed al-Sharaa.

The retaliatory strikes came one week after an ISIS gunman killed three Americans, including two Iowa National Guardsmen and a U.S. civilian interpreter.