The deployment of the air-to-air combat planes comes after two Russian warplanes, active in Syria, strayed into Turkish airspace last month, triggering strong condemnations from Turkey and its NATO allies. The U.S.-European Command in Stuttgart, Germany, said it had directed six fighter jets from the 48th Fighter Wing, based in England, to Incirlik, adding to other aircraft already sent to the base as part of the U.S.-led coalition against the Islamic State group in Syria.