Washington DC - Democratic lawmakers Monday urged the Pentagon to conduct an impartial probe of an attack on a school in Iran that left dozens dead, after allegations that American forces were to blame.

Iran has accused Israel and the US of conducting the strike on the elementary school in the southern city of Minab at the start of the war. The blast killed more than 150 people, most of them students.

President Donald Trump has blamed Iran, while the Pentagon has said it is investigating.

"Independent analysis credibly suggests the strike may have been conducted by US forces, which if true, would make it one of the worst cases of civilian casualties in decades of American military action in the Middle East," several high-ranking senators said in a joint statement.

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"The killing of school children is appalling and unacceptable under any circumstance," they added, saying the tragedy must be "fully and impartially reviewed" by Pentagon chief Pete Hegseth.

The New York Times says it has authenticated video uploaded by Iran's semi-official Mehr News showing a US Tomahawk cruise missile striking a structure described as a clinic inside a Revolutionary Guards' base next to the school.

According to the Times, in this war, the only military using Tomahawks is the US.

The Times previously reported that US military statements indicating forces were attacking naval targets near the strategic Strait of Hormuz, where a Revolutionary Guards' base is located, "suggest they were most likely to have carried out the strike."

The lawmakers said the incident is all the more worrisome given what they called Hegseth's "openly cavalier approach" to the use of force. He said last week US strikes in Iran wouldn't be bound by "stupid rules of engagement."

The statement's signatories included Jeanne Shaheen, the top Democrat on the Senate Foreign Relations Committee.

Human Rights Watch has since called for the massacre to be investigated as a war crime.