Pentagon officials said the Americans were not involved in any combat role on the ground. A Syrian militia commander told the photographer that the American troops had fired missiles from the rooftop of a house to destroy a booby-trapped car in the village, a characterization that Pentagon officials challenged.

“We have been conducting advise-and-assist operations with elements of the Syrian Democratic Forces for many weeks,” Col. Steve Warren, the chief military spokesman in Baghdad, said in an email. “Nothing has changed in our relationships or our distance from the front lines of combat.”

Colonel Warren said the American commandos in the photographs were operating east of the Euphrates River, an area where he said Syrian Kurdish and Arab fighters had been operating.