Russian and Syrian forces "accidentally" bombed U.S.-backed fighters in Syria on Tuesday, killing some Syrian rebels, a top U.S. general said Wednesday.

A joint operation targeting Islamic State (ISIS) militants near the village of al-Bab sent missiles at Syrian coalition troops instead, according to Army Lt. Gen. Stephen Townsend.

"Yesterday, we had some Russian aircraft and regime aircraft bomb some villages that I believe they thought were held by ISIS," Townsend said. "Yet, they were actually—on the ground were some of our Syrian Arab Coalition forces."

U.S. forces on the ground less than three miles from the site reportedly observed the strike and alerted the Russian military through an emergency line, after which the bombing stopped, he continued.

The Russian ministry has denied Townsend's claim. The state-run outlet Russia Today quoted a statement from the ministry that read, "Not a single air strike on the regions specified by the U.S. side was conducted by Russian or Syrian air forces."

Russia deployed aircrafts to Syria in late 2015 to aid President Bashar al-Assad in the fight against ISIS, while U.S. troops support the Syrian opposition forces, and the two sides set up a communication channel to avoid getting into each other's air space.