The United States has expressed concern over reports that Israel used US-supplied white phosphorus munitions in an attack in southern Lebanon in October, Sky News reported.

“We’ve seen the reports,” White House spokesman John Kirby told reporters on Air Force One. “We are certainly concerned about this. We’re going to ask questions to try and find out a little bit more.”

He added that white phosphorus has a “legitimate military use” for lighting and creating smoke to conceal movement.

“Obviously, any time we provide items like white phosphorus to other militaries, we require that they be used in accordance with those legitimate purposes … and in accordance with the law of armed conflict,” he said.

What is white phosphorus?

It is a waxy solid chemical that ignites instantly when it comes into contact with oxygen.

It sticks to surfaces such as skin and clothing and can cause serious injury.

Chemicals that remain in the body can damage internal organs and even cause death.

What is reported?

The report first appeared in The Washington Post, which said at least nine civilians were injured in the incident.

At least three people were taken to hospital.

The Post adds that at least four houses were burned.

Amnesty International told the newspaper that the incident should be investigated as a war crime, while the executive director of Human Rights Watch said the report should be taken seriously enough to “reevaluate US military aid to Israel”.