The United States is concerned about reports Israel used US-supplied white phosphorus munitions in an October attack in southern Lebanon, White House spokesperson John Kirby said on Monday.

“We’ve seen the reports. Certainly concerned about that. We’ll be asking questions to try to learn a little bit more,” Kirby told reporters on Air Force One.

Kirby said white phosphorus has a “legitimate military utility” for illumination and producing smoke to conceal movements, Reuters reported.

“Obviously any time that we provide items like white phosphorus to another military, it is with the full expectation that it will be used in keeping with those legitimate purposes … and in keeping with the law of armed conflict,” he said.

Israeli Defense Minister Yoav Gallant, asked about the report that Israel used white phosphorus in Lebanon, said the Israeli army “and the entire security establishment acts according to international law. That is how we have acted and how we will act.”