BENGHAZI - Forces allied to Libya's eastern government carried out air strikes on Islamic State militant areas of Derna city, but an aircraft later crashed because of mechanical failure, a spokesman said on Monday.Libyan National Army forces, led by Gen. Khalifa Haftar, carried out an air strike on the Hay Arrbamiya area of Derna, a city that has been the scene of fighting between Islamic State militants and rival Islamist fighters.An eyewitness in the city confirmed an airstrike on Derna in the area controlled by Islamic State but could not give details on any damage or casualties.