The US has admitted carrying out an attack in eastern Syria that killed dozens of Syrian forces fighting so-called Islamic State (IS).
The US-led coalition said the “mistake” on 17 September was intended to target IS positions.
Coalition aircraft from the UK, US, Denmark and Australia were involved in the attack near Deir al-Zour.
Syrian President Bashar al-Assad has maintained that the deadly airstrikes were intentional.
The attack, which the Russian army says killed at least 62 Syrian troops, were halted when Russia informed the US it was hitting Syrian forces.
“In this instance, we did not rise to the high standard we hold ourselves to, and we must do better than this,” said US Lieutenant-General Jeff Harrigian.
A spokesman for US Central Command (Centcom), the wing of the American military in charge of all its Middle East forces, said the mistake was “regrettable”, adding that it was not the intent to target Syrian troops.
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However, President Assad said he did not believe the US account that the attack “wasn’t an accident”.
“It was four aeroplanes that kept attacking the position of the Syrian troops for nearly one hour, or a little bit more than one hour,” President Assad told the AP news agency.
A spokesman for the UK Ministry of Defence said Tuesday’s report showed that the decision to carry out strikes near Deir al-Zour was “made in good faith”.
“We welcome the coalition’s report and its conclusion that the decision to identify the targets as Daesh (IS) fighters was reasonable,” he said.
“We would not and did not intentionally strike known Syrian Regime military units,” he added.