US Air Force Brig. Gen. Richard Coe who is investigating the incident said that the mistake was mostly based on "human factors."
"In this incident, ultimately, we made an unintentional regrettable error primarily based on human factors in several areas in the targeting process," Coe told reporters during a press briefing.
"We’ve got the F-16s, A-10s, FA-18s and also remotely piloted aircraft as well," Coe told reporters when asked what type of aircraft got involved in the attack.
The Pentagon also said that the US-led coalition's strikes on Syrian army positions would have continued if Russian military officials did not call their colleagues via a deconfliction channel. The deconfliction channel is part of a memorandum of understanding on safety of flights in Syria's airspace signed by the US Defense Department and Russian Ministry of Defense in October 2015.
Coe explained the coalition had given Russia prior notice about the airstrike, but provided inaccurate information, erroneously identifying the target as being 9 kilometers (5.6 miles) south of the Deir ez-Zor airfield instead of 9 kilometers south of the city.
"We would not have stopped the strikes but for the phone call from the Russians," Coe told reporters. "Without that call from the Russians the strikes would have continued for longer than they did, so we’re certainly grateful for that phone call."
Had the US-led coalition given the correct information, Russia would have had the opportunity to warn the coalition that Syrian forces were operating in the area, Coe added.
The United States will discuss compensation for victims of the September airstrike on government forces in Deir ez-Zor upon a request from Syrian authorities, US Central Command spokesman Col. John Thomas said.
"Should the government of Syria make a formal claim for compensation against the United States, such a claim will be addressed through appropriate diplomatic channel," Thomas told reporters.
Russian officials waited for almost half an hour to pass information on US-led coalition strike mistake in Syria’s Deir ez-Zor through the deconfliction channel, the US Central Command (CENTCOM) claimed.
"There was a critical delay of 27 minutes while Russian officials waited for a familiar US counterpart to come on the line before passing that information," the release stated.
Brig. Gen. Richard Coe, who led the probe into the incident, recommended enhanced use of the deconfliction channel with Russia "to ensure that critical information is communicated more quickly to available personnel," according to the release. Coe has told reporters in a conference call that the United States had asked Russia to convey messages immediately regardless of who is on the line.
The full Pentagon's report into the deadly strike remains classified, the spokesman said.
Earlier, the Russian Defense Ministry slammed the US-led coalition for striking civilians instead of terrorists.
"Weddings, funerals, hospitals, police departments, humanitarian convoys and even Syrian troops, fighting against Daesh terrorists near Deir ez-Zor, become targets for coalition airstrikes," spokesman Maj. Gen. Igor Konashenkov said, commenting on an alleged US-led coalition's member's strike on a Syrian village in north Aleppo that claimed at least six lives.