Washington DC - A top commander of US forces in the Middle East avoided taking responsibility Tuesday for an attack on a school in Iran that left 155 people dead on day one of the war, insisting a "complex" probe continues.

Admiral Brad Cooper, the commander of US Central Command, told a congressional oversight panel that "the school itself is located on an active IRGC cruise missile base," making the investigation "more complex than the average strike." IRGC stands for Iran's Islamic Revolutionary Guard Corps.

The attack killed 73 boys, 47 girls, 26 teachers, seven parents, a school bus driver, and another adult in the southern city of Minab on February 28, according to Iranian state media.

The US has repeatedly avoided assuming responsibility for the tragedy.

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Cooper was responding to questioning by House Armed Services Committee Ranking Member Adam Smith, a Democrat, who said that, "in the past, when we've had these types of mistakes, they have been quickly acknowledged, even if a further investigation is necessary."

Cooper promised to share the results of the investigation when it was complete. Smith responded by saying, "So that's a 'no.' We will not take responsibility for something we very obviously did."

The New York Times has previously reported that the school was hit by a US Tomahawk cruise missile, a weapon which Iran does not possess. CNN has also reported that the US was responsible for the attack.

President Donald Trump initially claimed that Iran itself might be behind the attack because "they have no accuracy whatsoever" with their munitions.

House Democrats filed impeachment proceedings against Defense Secretary Pete Hegseth in the wake of the attack, although this was largely seen as symbolic given Republican control of the chamber.

Iran first claimed that more than 175 teachers and students were killed, before later revising the death toll.

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AFP has been unable to access the location to independently verify details reported by Iranian media.

Israel has consistently denied any involvement in the attack.

US officials, including military leaders, have repeatedly said they do not target civilians.