Three MQ-9 Reaper drones the U.S. military said had been "harassed" by Russian fighter jets over Syria on Friday were the same drones that later carried out an airstrike that killed a top Islamic State group leader, U.S. Central Command announced Sunday.
IS leader Usama-al-Muhajir was killed on Friday, CENTCOM said.
The news capped three straight days of tense encounters where the U.S. had criticized Russian pilots for "unsafe and unprofessional" behavior with its drones flying over Syria.
"The strike on Friday was conducted by the same MQ-9s that had, earlier in the day, been harassed by Russian aircraft in an encounter that had lasted almost two hours," Sunday's CENTCOM statement added.
The U.S. military has criticized the behavior of Russian fighter pilots it said had "harassed" Reaper drones that were flying anti-terrorism missions over Syria in two separate incidents on Wednesday and Thursday.
To highlight that behavior, the U.S. military declassified two videos that showed Russian fighter jets dropping parachute flares in front of the drones and one of the jets engaging its afterburners, all actions that led the drones to have to take evasive maneuvers.
There was a third straight day of interactions between Russian fighters and U.S. drones on Friday when U.S. Air Forces Central said "Russian aircraft flew 18 unprofessional close passes that caused the MQ-9s to react to avoid unsafe situations."
"We have made it clear that we remain committed to the defeat of ISIS throughout the region," said Gen. Michael "Erik" Kurilla, commander of CENTCOM. "ISIS is a threat, not only to the region but well beyond."
"There are no indications that any civilians were killed in this strike and the coalition is assessing reports of a civilian injury," said the CENTCOM statement on Sunday.
It is unclear where in Syria the U.S. airstrike had occurred.
U.S. aircraft normally operate in eastern Syria where 900 U.S. troops are involved in counter-IS operations, while Russian troops and aircraft operate in western Syria in support of President Bashar al-Assad's regime.
Last week, a Pentagon spokesman discounted Russian Defense Ministry claims that American drones had been operating in areas where Russian aircraft operate.
However, on previous occasions U.S. aircraft have operated in northwestern Syria to undertake airstrikes targeting senior IS leaders.
For years, both militaries have regularly used a deconfliction safety line to provide advance notifications of where their aircraft would be operating over Syria to prevent any unsafe interactions.
U.S. officials have said that Russia is no longer using that line regularly in recent months.