An investigation has found air strikes by the US-led coalition that reportedly killed dozens of troops fighting for the Syrian government did not violate international law, the US military said.

The targets of the strikes near the Syrian city of Deir Az Zor were misidentified as ISIL fighters on September 17, but they turned out to be loyalists of the Syrian army, the US Air Forces Central Command said in a statement on Tuesday.

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"Although air strikes likely hit forces aligned with the government of Syria, the strikes were conducted under a good faith belief that the strikes were targeting Daesh, in accordance with the law of armed conflict and the applicable rules of engagement," it said, using an Arabic acronym for Islamic State of Iraq and the Levant.

It added that evidence showed there wasn't "a deliberate disregard of targeting procedures or the rules of engagement".

Russia said 62 Syrian soldiers were killed and at least 100 more wounded. The attack was the first known direct strike by the US-led coalition on forces loyal to Syrian President Bashar al-Assad.

Brigadier General Richard Coe, the investigating officer, said a number of "human factors" contributed to the misidentification. 

"In my opinion, these were a number of people all doing their best to do a good job," Coe said. "In many ways these forces looked and acted like the Daesh forces the coalition has been targeting for the last two years."

Al Jazeera's Rosiland Jordan, reporting from Washington DC, said there was no information on whether anyone was being punished for the series of human errors that led to the deadly incident.

She also noted prior to the attack the coalition tried to communicate information about the planned air raid with Russia to make sure Russian or Syrian fighter jets would not be in the area getting in their way.

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The Russians were not able to get back in touch with their coalition point of contact on time, she said.

"When the coalition found out that the targeted fighters were known to the Russians, the strikes stopped," said Jordan.

The United States, Australia, Denmark and Britain participated in the attack.

Syria denounced the air strike and said it was "conclusive evidence" of US support for ISIL, calling it "dangerous and blatant aggression".

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Source: Al Jazeera News