Iran announced Tuesday that it has put the elite Revolutionary Guards in charge of defending the country's territorial Persian Gulf waters in what appeared to be a hardening of its stance in the vital oil route.

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 several small confrontations in Hormuz that the Americans blamed on provocations by Guards ships.

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. No reason was given for the move, but it could be aimed at showing Iran is serious in its warnings of retaliation for any attack.

Gen. Yahya Rahim Safavi, the top military adviser of Iran's supreme leader Ayatollah Ali Khamenei, announced that "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 Guards head until earlier this year, warned that all vessels in the Gulf are within the range of Iranian missiles.

"No warship can pass through the waterway without being in our range," he said, quoted by the state news agency IRNA. "Our armed forces, possessed with defensive weapons including missiles ... and torpedoes, are able to control the strait of Hormuz."

A spokesman for the Bahrain-based U.S. 5th Fleet, Lt. Nathan Christensen, said the move will not significantly affect U.S. Navy patrols in the Gulf. The fleet's task is to keep the Hormuz Strait open to ensure "free flow of trade and commerce," he said.

"We are not interested in a confrontation in the Gulf," said Christensen. He said the Navy expects "responsible and professional maritime behavior" from all vessels, including the Revolutionary Guards.

The U.S. Navy currently has one aircaft carrier in the Gulf and normally keeps some three dozen warships and auxiliary vessels. U.S. warships regularly speak to Iranian military ships in the Gulf to coordinate. Now they will have to do so with the Guards, which the U.S. has declared a terrorist organization, security analyst Riad Kahwaji said.

"It's now the hardline, radical force that has taken the lead in military matters, not just in political affairs of Iran," said Kahwaji, of the Dubai-based Institute for Near East and Gulf Military Analysis.

Safavi repeated warnings that Iran would retaliate against U.S. bases in the Gulf if Israel launches a strike against Iran.

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' 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.