Any spy craft in the Gulf of Oman and the Indian Ocean where a trilateral naval drill is being held by Iran, Russia and China will be attacked, said Deputy Chief of Iran's Army for Coordination Rear Admiral Habibollah Sayyari on Saturday, according to the Iranian Tasnim News."Many countries are definitely seeking to know what the matter is. Spies have also taken action," said Sayyari. "A joint war game is no joke, and this is no joking matter for us either. We will hit whatever spying craft in the war game zone, be it watercraft or aircraft, as we have proved having such a capability in the past." While some of the information about the exercise will be published, all classified information will remain inaccessible, according to Sayyari.The trilateral exercise, named Marine Security Belt, will take place over four days.In November, Iranian forces shot down a foreign drone over the port city of Mahshahr in its southern Khuzestan province, state news agency IRNA reported.In June, Iran shot down an unmanned US surveillance drone, which the Revolutionary Guards said was flying over southern Iran. Washington said the US drone had been shot down by Iran in international airspace over the Strait of Hormuz in the Gulf."The message of this exercise is peace, friendship and lasting security through cooperation and unity... and its result will be to show that Iran cannot be isolated," Iranian flotilla admiral Gholamreza Tahani said on state television.The broadcaster said the drills included rescuing ships on fire or vessels under attack by pirates and shooting exercises.The Gulf of Oman is a particularly sensitive waterway as it connects to the Strait of Hormuz, through which about a fifth of the world's oil passes and which in turn connects to the Gulf.Washington proposed a US-led naval mission following several attacks in May and June on international merchant vessels, including Saudi tankers, in Gulf waters which the United States blamed on Iran. It denies the accusations.Reuters contributed to this report.