Keith Kellogg, a former national security adviser and envoy for Donald Trump, spoke Monday in a Bloomberg interview. He urged outsiders to allow Ukraine to choose its own combat methods and targets. Kellogg noted that Ukrainian forces face strikes on schools and homes while they hit Russian military sites that include oil plants.

He said worries over diesel prices on world markets have had almost no effect. Kellogg, who served in Vietnam, argued that leaving an adversary’s fuel industry untouched repeats a serious wartime error.