CHICAGO — An Illinois Army National Guard soldier vowed to bring “the flames of war to the heart” of America if he was unable to get to the Middle East to join the Islamic State group, and his cousin bragged he could kill up to 150 people in a terrorist attack in the U.S., federal prosecutors said Thursday in announcing the men’s arrests. Both are also accused of hatching a plot to attack a U.S. military facility.

Hasan R. Edmonds, the 22-year-old guardsman, was arrested Wednesday evening at Chicago Midway International Airport trying to board a plane on the first leg of a journey to Egypt. Jonas M. Edmonds, 29, was detained a few hours later at home, the U.S. attorney’s office in Chicago said. Both men are U.S. citizens from suburban Aurora.

An unsealed federal complaint says the plan was for Jonas Edmonds to carry out an attack in the U.S. after Hasan Edmonds left the country, donning Hasan’s uniform to gain better access to soldiers. The complaint says they plotted an armed attack against a U.S. military facility in northern Illinois where Hasan Edmonds had trained. The complaint did not name the facility.

A spokesman for the Illinois National Guard, Lt. Col. Brad Leighton, said Hasan Edmonds was member of Golf Company 634th Brigade Support Battalion, based in Joliet.

In Internet messages to an undercover FBI agent in January, Hasan Edmonds said that if he was unable to make it to the Middle East, he would help bring “the flames of war to the heart” of America and “cause as much damage and mayhem as possible,” the complaint says.