Rice said a planned U.S. missile defense shield, to be partly based in the Czech Republic and Poland, would dampen any threat of an attack from Iran. Russia opposes the project.
"We also are able to look to the future of a missile defense system that will make it more difficult for Iran to threaten (and) and be bellicose and say terrible things because their missiles won't work," Rice said.
Iranian state TV and radio said the Revolutionary Guards -- the ideologically driven wing of Iran's armed forces -- had fired ground-to-sea, surface-to-surface and sea-to-air missiles overnight. Long-range missiles were also launched.
CHINA URGES RESTRAINT
"The ... maneuver brings power to the Islamic Republic of Iran and is a lesson for enemies," Guards Commander-in-Chief Mohammad Ali Jafari was quoted as saying.
Iran has threatened to shut the Strait of Hormuz, a vital route for Gulf oil exports, if it is attacked. Thursday's exercises involved divers and speedboats, as well as the launch of a high-speed torpedo called Hout, state media said.
Commenting on Iran's Gulf maneuvers, Kuwait said it hoped wisdom would prevail on all sides. "The region has had enough of continuous wars," Kuwaiti Foreign Ministry Undersecretary Khaled Jarallah was quoted by state news agency KUNA as saying.
On Iranian threats to close the Strait of Hormuz, he said: "We hope it does not come to this."
The missile tests rattled global oil markets, pushing up the price of oil. Crude prices have dipped in recent days but have hit a series of record highs this year partly on Iran tensions.