WASHINGTON (CNN) -- The United States imposed stiff sanctions against Iran on Thursday, targeting two Iranian military groups and a number of Iranian banks and people it accuses of backing nuclear proliferation and terror-related activities.
"What this means is that no U.S. citizen or private organization will be allowed to engage in financial transactions with these persons and entities," Secretary of State Condoleezza Rice said. "In addition, any assets that these designees have under U.S. jurisdiction will be immediately frozen."
Rice and Treasury Secretary Henry Paulson made the announcement in a brief appearance before reporters on Thursday morning.
Rice accused Iran of "pursuing nuclear technologies that can lead to a nuclear weapon; building dangerous ballistic missiles; supporting Shia militants in Iraq and terrorists in Iraq, Afghanistan, Lebanon and the Palestinian territories; and denying the existence of a fellow member of the United Nations, threatening to wipe Israel off the map." Watch Rice tell why sanctions are being imposed »
"Many of the Iranian regime's most destabilizing policies are carried out by two of its agencies: the Islamic Revolutionary Guard Corps, or the IRGC, and the Quds force, an arm of the IRGC," she said.
She said the sanctions were being imposed "because of the Revolutionary Guard's support for proliferation and the Quds force support for terrorism."
The United States also designated three Iranian state-owned banks for sanctions, two of them "for their involvement in proliferation activities" and the other "as a terrorist financier," Rice said.
"Iran funnels hundreds of millions of dollars each year through the international financial system to terrorists," Paulson said. "Iran's banks aid this conduct using a range of deceptive financial practices intended to evade even the most stringent risk management controls."
The Revolutionary Guard Corps, he said, "is so deeply entrenched in Iran's economy and commercial enterprises, it is increasingly likely that, if you are doing business with Iran, you are doing business" with the corps.
"We call on responsible banks and companies around the world to terminate any business with Bank Melli, Bank Mellat, Bank Saderat, and all companies and entities" of the corps, Paulson said.
The move marks the first time the United States has attempted to punish another country's military through sanctions.
Previous sanctions imposed by the United States have been tied to Iran's nuclear program. The United States has been working with other world powers to halt what they believe is Iran's intent to develop a nuclear arsenal. Iran says it is pursuing nuclear power for peaceful reasons.
Mohamed ElBaradei, director-general of the United Nations' International Atomic Energy Agency, said last month that Iran's declared nuclear material has not been diverted from peaceful use and criticized U.S. rhetoric regarding Iran.
The Quds Force is blamed by the U.S. military for training and arming Shiite militias in Iraq and smuggling highly lethal explosives into Iraq, where they are used to attack coalition forces. Iran denies the charge.
"If the Iranian government fulfills its international obligation to suspend its uranium enrichment and reprocessing activity, I will join my British, French, Russian, Chinese and German colleagues, and I will meet with my Iranian counterpart any time, anywhere," Rice said. "We will be open to the discussion of any issue. But if Iran's rulers choose to continue down a path of confrontation, the United States will act with the international community to resist these threats of the Iranian regime."
Last month, representatives of world powers announced that unless a November report shows a "positive outcome" of talks with Iran about its uranium enrichment program, they will move ahead with plans for a resolution imposing additional sanctions on the country.
The U.N. Security Council has repeatedly demanded that Iran suspend enrichment of uranium and has imposed limited sanctions on Tehran for refusing to comply. The European Union is weighing its own unilateral sanctions. E-mail to a friend
CNN's Kathleen Koch and Elise Labott contributed to this report.