From NightWatch:

Syria-Syria Kurds-US: On 19 August, the Syrian air force conducted the first air attacks and Syrian Kurdish People’s Protection Units (YPG) militiamen in Hasakah Governate. Ground fighting intensified late on the 19th when Kurdish YPG fighters battled Syrian forces.

“The clashes continue in areas inside the city today (20 August). There were military operations,” a Kurdish official said.

On the 19th, also for the first time, US combat aircraft flew what the Pentagon called protective patrols around Hasakah to prevent Syrian jets from attacking US special forces personnel, who are operating on the ground with the Syrian Democratic Forces (SDF).

Comment: The Syrian Kurdish militias are the major component of the SDF. The US protective patrols are the first sorties of their kind in the war.