The US Defense Department says mid-September airstrikes that killed dozens of Syrian soldiers in the country's eastern province of Dayr al-Zawr were an “unintentional error” and did not violate international law.

The Pentagon made the claims in a statement on Tuesday, saying that the US-led coalition had launched the air raids based on wrong intelligence.

"The evidence showed there was not a deliberate disregard of targeting procedures or the rules of engagement," the statement said. “The decision to strike these targets was made in accordance with the law of armed conflict and the applicable rules of engagement."

On September 17, two F-16 and two A-10 jets entered Syrian air space from Iraq and carried out four attacks. Reports said that the air raids were conducted by American, Australian, Danish and British warplanes.

At least 90 Syrian soldiers lost their lives in the strikes.

“We made an unintentional, regrettable error, based on several factors in the targeting process,” said Richard Coe, US air force brigadier general and the investigating officer.

Coe claimed that during his six-week probe he found “no intent to target Syrian [government] forces”.

The US military confirmed the report at the time, saying it halted the attack after Russian officials said the targets were Syrian government forces and not Daesh Takfiri militants.

Immediately after the US attack, Daesh terrorists launched a major offensive in the region and briefly took control of it before Syrian forces managed to retake it.

Moscow and Damascus accused the US of deliberately attacking government troops to boost Daesh.

The photo taken on November 12, 2015 shows an F-15E Strike Eagle before departing from the UK to join the US-led coalition purportedly striking Daesh positions in Syria. (Photo by AFP)

US warplanes have been conducting airstrikes against Daesh in Iraq since August 2014. Some Western states have also participated in some of the strikes in Iraq.

Since September 2014, the US and some of its allies have been carrying out airstrikes against Daesh inside Syria without any authorization from Damascus or a UN mandate.

The US-led coalition has done little to stop Daesh's advances in Syria and Iraq. Some analysts have criticized the military campaign, saying the strikes are only meant to benefit US weapons manufacturers.

Syria has been gripped by a foreign-backed militancy since March 2011 and Daesh terrorists still control parts of the country and neighboring Iraq.

According to UN Special Envoy for Syria Staffan de Mistura, more than 400,000 people have been killed in the conflict in Syria and about 23 million displaced within or beyond the Arab country’s borders. The UN has stopped its official casualty count in Syria, citing inability to verify the figures it receives from various sources.