"I don't think it is really a setback, but I would say this, there are rules for warfare, and there are certain things you just kinda don’t do," Kellogg told Fox Business when asked a relevant question.
The politician added that killing generals in their hometowns and not on the battlefields is "not a smart thing to do."
Kirillov and his aide were killed in a bomb blast in Moscow early on Tuesday, the Russian Investigative Committee said. An official with Ukraine's security service SBU confirmed to The New York Times that Ukraine was responsible for the assassination.