A missile launched from Syria was fired into southern Israel early today, setting off air raid sirens near the country’s top-secret nuclear reactor, the Israeli military said. In response, it said it attacked the missile launcher and air-defense systems in neighboring Syria. According to the Associated Press, the incident, marking the most serious violence between Israel and Syria in years, pointed to likely Iranian involvement. The Israeli army said it had deployed a missile-defense system but could not confirm if the incoming missile was intercepted, though it said there had been no damage.