Iran, embroiled in a standoff with the West over its nuclear ambitions, has said it could respond to any military attack by closing the strait at the southern end of the Gulf through which about 40 percent of the world's traded oil passes.
The United States, whose Fifth Fleet is based in the Gulf state of Bahrain, has vowed to keep shipping lanes opened.
The West accuses Tehran of seeking to build nuclear warheads but Iran, the world's fourth largest oil producer, insists its aim is to master technology to make electricity. Washington has not ruled out military action if diplomacy fails to end the row.
"At a time of war no ship can pass through the region of the Persian Gulf without being in the reach of the Revolutionary Guards' coast-to-sea missiles," Yahya Rahim-Safavi, a senior military adviser of Supreme Leader Ayatollah Ali Khamenei, was quoted by the Iran daily as saying.
Rahim-Safavi earlier this week said Khamenei had put the elite Guards in charge of defending the Gulf against any enemy attacks and that they would not hesitate to "confront foreign forces."
The comments came amid persistent speculation about a possible U.S. or Israeli strike on Iran's nuclear facilities.
Iran has dismissed reports of possible U.S. or Israeli plans to strike the country, but says it would respond by attacking U.S. interests and Israel if any such assault was made.
Iran's air force and defense units held war games this week to test equipment and boost readiness, Iranian media reported.
Alongside the regular army, Iran has a Revolutionary Guards force viewed as guardians of the Islamic ruling system.
The Guards have a separate command and their own air, sea and land units. They are deployed on sensitive border regions and guard key institutions and their arsenal includes the Shahab-3 missile, which reports say can reach targets in Israel.
(Reporting by Zahra Hosseinian, writing by Fredrik Dahl; Editing by Charles Dick)
