The United States was responsible for a Tomahawk missile strike on an Iranian elementary school because of a targeting mistake, The New York Times reported on Wednesday.

The newspaper, citing US officials, said the investigation into the 28 February attack was ongoing but preliminary findings were that the United States was responsible.

The US military was conducting strikes on an adjacent Iranian base of which the school building was formerly a part and target coordinates were set using outdated data, it said.

President Donald Trump suggested earlier this week that Iran itself may have been responsible but later said he could "live with" whatever the investigation reveals.

Asked by reporters about the Times report on Wednesday, Trump said: "I don't know about it."