ERBIL, Iraq — Turkish warplanes bombed Kurdish fighters in Iraq and Syria on Tuesday in an unusually intense operation that presented a new complication for the United States’ military campaign against the Islamic State.

The Turkish military’s targets included the Y.P.G., a Kurdish militia that has played an important role in the American-backed operations in Syria against the Islamic State, also known as ISIS or ISIL.

Adding to the tensions in the region, Kurdish officials said one Turkish airstrike had mistakenly struck Kurdish pesh merga troops on Mount Sinjar in northwestern Iraq, killing at least five and wounding more, some critically.

The pesh merga in Iraq’s autonomous region carried out the opening attacks in the offensive to retake Mosul from the Islamic State, and they have been an American ally in operations against the militants.