A top US commander has warned Russia and Syria he will defend US special operations forces in northern Syria if the country's regime attacks again areas where troops are located.

Lieutenant General Stephen Townsend, commander of American troops in Iraq and Syria, made the comment days after warplanes from the President Bashar al-Assad's regime attacked an area where US special operations forces were operating.

The US forces were deployed in the area to support Kurdish forces – a key ally of the US in the conflict in Syria.

"We've informed the Russians where we're at… (they) tell us they've informed the Syrians, and I'd just say that we will defend ourselves if we feel threatened," Townsend told CNN.

He also added he hopes the US can defeat the so-called Islamic State (Isis/Daesh) terror group in Iraq and Syria in the next year.

"Do I think ISIL [Isis] will be gone from Iraq and Syria? No. But I want them out of the cities," he said.