About 8,000 military military personnel are participating in a drill to test Iran\'s air-defense systems, an official said. The four-day exercise, called Velayet-4, began Monday. \"Various kinds of fixed, mobile and tactical long-range radars and fixed, tactical and airborne electronic surveillance systems will participate in this exercise,\" said Farzad Esmaili, head of Iran\'s air defense operations, IRNA reported. Bomber jets, refueling planes and unmanned surveillance aircraft are also involved in the exercise, he said. The drill covers the entire eastern sector of the country. Participants include soldiers from the regular army and Revolutionary Guards Corps, Iranian media reports said. Brig. Gen. Shahrokh Shaharam told the Tehran Times new defense systems were to be used for the first time during the exercise.