An unarmed US drone flying over the Gulf was trailed by an Iranian jet, dpa quoted the Pentagon as saying Thursday.The incident occurred Tuesday over international waters,broadcaster CNN reported, citing Defence Department spokesman George Little.The Iranian jet never got closer than 26 kilometres to the drone.No shots were fired.Two US fighter planes were escorting the drone on a \"routine classified\" surveillance mission when the Iranian jet appeared, news reports said.\"The United States communicated to the Iranians that we will continue to conduct surveillance flights over international waters consistent with long-standing practice and our commitment to the security of the region,\" Little said.The drone was an MQ-1 Predator.The F-4 is a Vietnam War-era,US-made fighter jet