The United States has reached the preliminary conclusion that Russian warplanes bombed an aid convoy and warehouse belonging to the Syrian Arab Red Crescent, two American officials told CNN on Tuesday.
"All the evidence we have points to that conclusion," one of the officials said.
The aid convoy was hit Monday night in the area of Urum al-Kubra, west of Aleppo, prompting the United Nations to halt its aid operations in Syria.
The International Committee of the Red Cross said that around 20 civilians were killed as well as the director of the Red Crescent's Urum al-Kubra branch, Omar Barakat.
The aid was intended for eastern Aleppo, where an estimated 250,000 civilians have been short of food, medicine and water, noted CNN.
UN Secretary General Ban Ki-moon called Monday night's attack "sickening, savage and apparently deliberate."
"Just when we think it cannot get any worse, the power of depravity sinks lower," Ban was quoted as having told world leaders convening at the UN General Assembly annual meeting Tuesday.
Rebels, locked in a vicious civil war with the Syrian government, reportedly hold the area where the convoy was struck. Russia has been helping its close ally President Bashar Al-Assad in the fight, though it has said its efforts are focused on attacking terror groups such as Islamic State (ISIS) ISIS that have flourished during the conflict.
Russian Defense Ministry spokesman Igor Konashenkov said on Tuesday that analysis of video footage from drones of the strike show that militants were following the convoy, according to the Russian state news site TASS.
"It is clearly seen in the video that a terrorists' pickup truck with a towed large-caliber mortar is moving along with the convoy," he claimed.
The attack on the convoy came hours after a ceasefire brokered by the United States and Russia officially came to an end, and sections of Aleppo held by rebel forces were shelled.
Following the attack, the U.S. military had been reviewing classified radar, signals and aerial surveillance intelligence.
Based on that and reports from the ground, it has concluded that only Russian warplanes were in position to attack this location when it happened, the official told CNN.
For now, there is no intelligence that specifically indicates Syrian aircraft or helicopters were in the area, though that type of information could later come to light, the official said.
The official added that it appears reports from the ground are accurate that were at least two waves of airstrikes, which is a common Russian military practice. Trucks inside the compound as well as those outside on the road were hit.