A Yemeni security official says four people were killed and 11 injured when the military plane they were on crashed shortly before landing at an air base in the country's south. It's unclear what caused Monday's crash but the official says it took place at al-Ammad air base near the southern city of Aden. The official says a technical problem might have caused the crash. He says there were eight Syrians and seven Yemenis on board. The official spoke on condition of anonymity because he was not authorized to speak to the media.