The World Health Organization has warned that "black rain" and toxic compounds in the air over Iran following US and Israeli airstrikes on oil facilities could cause respiratory problems.

The WHO, which has an office in Iran and works with local authorities on health emergencies, said it has received several reports this week of rain containing oil components.

"Black rain and the accompanying acid rain do pose a danger to the population, primarily to the respiratory system," WHO spokesman Christian Lindmeier told journalists in Geneva, adding that Iran has recommended people stay indoors. "Given the current risks, such as oil storage facilities and refineries that have been hit, causing fires and serious air quality problems, this is definitely a good measure."

He noted that the strikes have caused "a massive release of toxic hydrocarbons, sulfur oxides and nitrogen compounds into the atmosphere."