U.S. commanders in the Gulf have in the past said they find Guards ships more confrontational than the regular Iranian navy, which until the new order was responsible for Iranian defenses in the Gulf.
Iran has warned repeatedly that it will close the narrow Hormuz Strait at the mouth of the Gulf if the United States or Israel attacks it amid tensions over Iran's nuclear program. Around 40 percent of the world's oil passes through Hormuz. Last winter, Iranian and U.S. ships patrolling the Gulf had a series of small confrontations in Hormuz that the Americans blamed on provocations by Guards ships.
Gen. Yahya Rahim Safavi, the top military adviser of Iran's supreme leader Ayatollah Ali Khamenei, announced the change on the state news agency IRNA. He said "responsibility to defend the Persian Gulf" has been delegated to the Guards' navy, while the regular navy would operate in the Oman Sea, outside the Gulf and in the landlocked Caspian Sea.
Safavi, who was the head of the Guards until earlier this year, added a warning that all vessels in the Gulf are within the range of Iranian missiles.
"The Guards' missiles are able to cover the whole width of the Persian Gulf. No warship can pass through the waterway without being in our range," he said. "Our armed forces, possessed with defensive weapons including missiles, air, sea and torpedoes, are able to control the strait of Hormuz."
He also repeated warnings that Iran would retaliate against U.S. bases in the Gulf if Israel launches a strike against Iran.
"The Zionist regime doesn't have the necessary political, economic and social capabilities to start a big war," he said. If Israel attacks, U.S. forces in the region "will be put in serious danger. Definitely, the Americans don't want to get involved in a fourth front after conflicts in Afghanistan, Iraq and Georgia."
Israel, which is believed to possess a nuclear arsenal, has warned it would attack Iran to prevent the Persian state from acquiring nuclear weapons. The U.S. says it seeking a diplomatic solution, but has not ruled out military action. Iran denies it intends to develop nuclear weapons.
The Guards corps, which has land, navy and air components, is considered better equipped than the normal military and more ideologically fervent, tasked with protecting Iran's Islamic government, dominated by hard-line clerics.
The Guards' vessels stepped up patrols in Hormuz last year during a period when the U.S. had increased its naval strength in the Gulf, making a show of strength over Iran's defiance of U.N. resolutions on its nuclear program. The Guards say their navy vessels ask ships to identify themselves before entering the Gulf.
Despite last year's frictions, U.S. Navy and Iranian officials say their vessels are in frequent radio contact to avoid incidents in the waters of the narrow, heavily trafficked Gulf.