"That would include ethnic cleansing, it would include in particular indiscriminate artillery air and other fires directed at civilian population. That's what we're looking at right now. We haven't seen significant examples of that so far," the official said.

The United States will take penalizing action against Turkey if it engages in any "inhumane and disproportionate" moves against civilians during its incursion into northeastern Syria, a senior State Department official said on Thursday.