U.S. Airstrikes May Have Killed 64 Civilians, Says U.S. Central Command The actual number of civilian deaths is much higher, says observant group.

 LONDON -- U.S. airstrikes in Iraq and Syria may have killed 64 civilians and injured eight others in the past year, according to the U.S. Central Command -- the largest number the U.S. has confirmed to date.

The number of civilians killed in airstrikes is difficult to assess with certainty, and Central Command said they are unable to send investigators immediately. But, the department said they used what they believed was the highest possible number.

"If we see that a vehicle drives in after the weapons are released and all we can see is the vehicle and we don’t see any other civilians around it then we will say that there may have been as many as four or five civilians killed, not the minimum number, which would be the driver," Col. John J. Thomas, spokesperson for the U.S. Central Command, told ABC News.

He said that they consider external reports of deaths in areas where the U.S. operated, but don’t include those numbers if confirming evidence is not found.

But monitoring groups have reported a much higher number of civilians killed by U.S. airstrikes than Central Command has acknowledged, said Chris Woods, director of Airwars, a non-profit project that tracks international airstrikes in Iraq and Syria. The non-profit's data was part of what Central Command used in its new assessments.

Woods told ABC News that Airwars has tracked more than 1,800 likely civilian deaths by coalition airstrikes since August 2014, but the U.S. has confirmed only 119 civilian deaths in the same period of time.

"They are clearly now using other sources. But in order to make their final assessment, they are relying heavily on their own internal video and other intelligence sources," he said. "The problem with that is that those internal sources don’t see what’s going on down below on the battlefield."

On June 21, between 23 and 32 civilians were killed by airstrikes in Raqqa, Syria, according to Airwars –- and 21 of the civilians were named. The U.S. said three civilians were killed. Initially, the airstrikes were reported as Russian, but the U.S. has now taken responsibility for them.

"It has taken five months for us to find out that the U.S., not Russia, was responsible," Woods said.

Although he believes the U.S. assessments of civilian deaths are too low, he welcomed the new admission and noted that about half of the incidents now acknowledged by the U.S. were not known to the public before –- to Woods that shows that U.S. pilots and analysts are reporting information and showing concern about civilian deaths.

"Of the 13-member coalition, only the U.S. has admitted any casualty from its airstrikes," he said. "Effectively, the other members are hiding behind the coalition identity so they don’t have to do a proper investigation. They have to follow the American example and do much better."