Colorado senator Mark Udall has apologized for referring to slain journalists Steven Sotloff and James Foley to make a point in the course of a debate Saturday with his Senate opponent, Republican congressman Cory Gardner.

“When addressing ISIL during this weekend’s debate, I should not have invoked the names of James Foley and Steven Sotloff,” Udall said in a statement released Monday evening. “It was inappropriate and I sincerely apologize.”

Udall mentioned the late journalists in the course of a plea for deliberation and restraint on the part of the U.S. against the Islamic State. “I can tell you,” he said, “Steve Sotloff and James Foley would tell us, don’t be impulsive. Horrible and barbarous as those executions were, don’t be impulsive, come up with a plan to knock ISIL back.”

The senator said Monday that he meant merely to “emphasize the importance of taking the right next steps.” He came under fire for his remarks, which National Review Online reported Monday afternoon. Gardner, for his part, said that it’s “outrageous that Senator Udall would put words into the mouths of dead Americans.”