A US investigation into the missile strike on an Iranian girls' school won't cover up the truth, a US general said yesterday.

But the probe 'should have been done sooner', added General David Petraeus, former CIA director and commander of American forces in Iraq and Afghanistan.

At least 168 died, most of them schoolgirls, in the Tomahawk missile strike in Minab, southern Iran, on the first day of the conflict.

If the Pentagon confirms responsibility, it would be one of the worst cases of civilian casualties in decades of US military conflict in the Middle East. But Gen Petraeus told Radio 4's Today programme yesterday that rules he had established required the military to be 'first with the truth'.

He believed the Trump administration still respected those rules.

'We want to beat the bad guys to the headline,' he said. 'We want to get the headline instead of responding but we want to deal with the truth as we understand it at the time.

'Then we provide updates but we're not going to spin. We're not going to put lipstick on pigs. We're just going to lay it out.'

He said US Central Command had appointed 'a general officer from outside the command' to investigate the girls' deaths. 

Gen Petraeus added: 'This was a building that used to be part of an Iranian naval base but in recent years had been walled off and there was a play area and so forth and that might have been an indicator that it was not [a target]. 

'But I am very confident that once a general officer investigates this, what is coming from that will represent integrity.

'I hope that it is released to the public with an explanation that says, "Here's what took place, here's why it took place and here's what we're doing in the future to mitigate the chances of this happening again."'

He said he had been involved in a 'massive mistake' during Nato's bombing of the former Yugoslavia in 1999 'when we put three cruise missiles right through the Chinese embassy in Belgrade'.

He said that happened because an officer responsible for checking targets was away in Stuttgart in Germany on the day.

'These things happen,' he added. 'You tell the truth as you understand it and try to explain how it took place.'