Tension between Russian and U.S. forces in Syria has been heightened in recent weeks as both countries conduct patrols on the ground and in the air. The U.S. military said Russian fighter jets have been "harassing" American drones over Syria for the third day in a row this week.

On Wednesday, three U.S. MQ-9 drones were "engaged in unsafe and unprofessional behavior" by Russian aircraft. On Thursday, Russian fighter jets flew "incredibly unsafe and unprofessionally" against both French and U.S. aircraft over Syria.

And on Friday, the U.S. military said Russian aircraft had flown 18 unprofessional close passes that caused the MQ-9s to react to avoid unsafe situations. Rear Adm. Oleg Gurinov, head of the Russian Reconciliation Center for Syria, said earlier this week that the Russian and Syrian militaries have started a six-day joint training that ends Monday.

He warned that the increase of "uncoordinated flights" for the coalition’s drones leads to escalation and “Russia is not responsible for the safety of these flights.” Lt. Gen. Alex Grynkewich, head of U.S.

Air Forces Central Command, said in a statement that “We continue to encourage Russia to return to the established norms of a professional Air Force so we can all return our focus to ensuring the enduring defeat of ISIS.”

The U.S. and France are part of an international coalition fighting the Islamic State group, which once controlled large parts of Syria and Iraq. Despite the Islamic State group's defeat in Iraq in 2017 and in Syria less than two years later, the extremists still carry out deadly attacks in both countries.

In Syria, the 12-year conflict has left half a million people dead and over 1 million wounded. On any given day, at least 900 U.S. forces are in Syria, along with an undisclosed number of contractors, who partner with the Kurdish-led Syrian Democratic Forces.

Russia joined Syria’s conflict in September 2015 and has since helped tip the balance of power in favor of Syrian President Bashar Assad’s forces.

Russian warplanes still carry out attacks against the last major rebel stronghold in Syria’s northwest. Tension between Russian and U.S. forces has been heightened in recent weeks with the U.S. military accusing Russian fighter jets of "harassing" American drones over Syria.

On Friday, a drone attack by the U.S.-led coalition killed a man in northern Syria who was riding a motorcycle. The Syrian Observatory for Human Rights, an opposition war monitor, said the man was an Islamic State group militant.

Despite the increased tension, both sides have said they remain committed to avoiding a direct confrontation and are focused on taking down the Islamic State group.