The U.S. military on Friday dispatched two F-22 Raptors stealth fighter jets to intercept a pair of Syrian Su-24 Fencer aircraft that flew in the vicinity of Hasakah, Syria, according to news accounts citing an unnamed Pentagon official.

The American pilots of the fifth-generation fighters made by Lockheed Martin Corp. tried to radio the Syrian pilots but didn’t receive a response, according to CNN’s Barbara Starr.

The Raptors chased away the Fencers to protect U.S. Special Operations forces that are operating in the area, and no weapons were fired, according to The Los Angeles Times’ W.J. Hennigan.

The incident came a day after the U.S. scrambled fighters against Syrian Su-24s that bombed Kurdish forces operating near American special operations forces on the ground in the northeast part of the country in an incident that was the closest the U.S. has come to combat in the war-torn country, according to Military.com’s Richard Sisk.

The close encounter highlights how crowded the airspace and battlefield have become in the five-year-old civil war in Syria, where both U.S. and Russian forces are launching strikes with competing interests.

The U.S. has teamed with rebels to target militants affiliated with the Islamic State in Iraq and Syria, or ISIS, and has called for the removal of Syrian President of Bashar al-Assad, while Russian supports the regime.

Indeed, Syrian government warplanes were in the air again Saturday over the flashpoint northeastern city of Hasakeh, despite a U.S. warning against new strikes that might endanger its military advisers, Agence France Presse reported.

The U.S. has previously used the F-22 to intercept foreign military aircraft, from Russian Tupolev Tu-95 bombers off the coast of Alaska and California in 2015 to an Iranian F-4 Phantom warplane trying to intercept a U.S. MQ-1 Predator drone flying in international airspace off Iran in 2013