The US military killed an ISIS leader on Friday in a drone strike in eastern Syria, the US Central Command announced Sunday.

The strike, carried out by the same MQ-9 Reaper drones that were harassed by Russian aircraft earlier that day, killed Usama al-Muhajir, according to a press release.

"We have made it clear that we remain committed to the defeat of ISIS throughout the region," Gen. Michael "Erik" Kurilla, commander of CENTCOM, said in the release. "ISIS remains a threat, not only to the region but well beyond."

CENTCOM said no civilians were killed in the strike but it is assessing reports of civilian injury.

US drones participating in the anti-ISIS mission in Syria were harassed three times in as many days last week by Russian aircraft that are in Syria in support of President Bashar al-Assad.

The incident Friday between the Russian fighter jets and the US drones lasted for nearly two hours, a US Air Forces Central release said. Lt. Gen. Alex Grynkewich, commander of US Air Forces Central, said in the release that Russian aircraft "flew 18 unprofessional close passes that caused the MQ-9s to react to avoid unsafe situations."