The measures, announced by Secretary of State Condoleezza Rice and Treasury Secretary Henry Paulson, will cover some of the Iranian government's largest military and financial institutions, which Washington blames for supporting the Taliban in Afghanistan and Shia insurgent groups in Iraq, along with the Hamas and Hezbollah organizations, they said.
Also designated were several Iranian individuals and organizations. Secretary Rice said that any assets that these designees have under U.S. jurisdiction would be immediately frozen.
"They will provide a powerful deterrent to any international bank or company who thinks of doing business with the Iranian government," she said of the sanctions.
She also spoke directly to the Iranian people, saying the United States government had no conflict with them, and looked forward to aiding their ability to pursue "the peaceful use of nuclear power."
The announcement culminated a months-long series of harsh statements from both sides amid public recriminations both within the administration and the Congress over Tehran's strategic intentions. Rice on Thursday, for instance, repeated the administration's concern over statements indicating a desire in Tehran to "wipe Israel off the map."
CBS Evening News anchor Katie Couric asked the president of the Council on Foreign Relations, Richard Haass, about the effectiveness of U.S. sanctions against Iran, which have existed in various forms since 1979.
"Iran's economy is paying something of a price for these sanctions," Haass told Couric,"but it's not enough to just have sticks. You've also got to have some carrots, some incentives. So what's missing from this policy is not only international support for the sanctions, but what's missing from this policy is any sign of an incentive for Iran."
"I think this is the last effort that's going to be made diplomatically to bring Iran into the community of nations, if you will," terrorism expert Neil Livingstone, CEO of Executive Action, told CBS News correspondent Cami McCormick. However, for the sanctions to be truly effective, "we need other nations to also sign on and try the same thing."
As the Americans tightened their sanctions, Russian President Vladimir Putin said stronger international sanctions would make the Iranian situation more difficult to handle.
Speaking in Lisbon, Portugal, Putin said, "Why worsen the situation by threatening sanctions and bring it to a dead end? It's not the best way to resolve the situation by running around like a madman with a razor blade in his hand."
Rice, who also noted Iran's hardline anti-Israel stance, said the moves were part of "a comprehensive policy to confront the threatening behavior of the Iranians" but that Washington remains committed to "a diplomatic solution."
Iran has ignored previous, smaller attempts to apply international and financial sanctions, and says the conditions Washington has set for talks are unacceptable. Iran is continuing work on its nuclear program, which it says is peaceful.
Instead, officials said they hope the measures will increase pressure on Iran to take a deal offered last year that would give the oil-rich country economic and other incentives in exchange for dropping nuclear activities that could produce a bomb.
"There aren't a lot of other tools in the administration's tool box," Livingstone told McCormick, "other than going to some type of military action."
In Tehran, the Guards' chief, General Mohammad Ali Jafari, shrugged off increased U.S. pressure on the force.
"Today, enemy has concentrated sharp point of its attacks on the Guards," Jafari told a military ceremony in Mashhad, east of Tehran, according to the state news agency IRNA. "They have applied all their efforts to reduce the efficiency of this revolutionary body. Now as always, the corps is ready to defend the ideals of the revolution more than ever before."
Israel, on the other hand, said it was pleased with the sanctions.
"Israel welcomes the U.S. government's decision," Foreign Ministry spokesman Mark Regev said in Jerusalem. "We see this as an important contribution to the international effort to intensify pressure on Iran to abandon its nuclear program."
Paulson said it is nearly impossible for overseas businesses or banks to "know one's customer" in Iran and avoid unwittingly funding terrorism or other illicit activities.
State-owned banks Bank Melli, Bank Mellat and Bank Saderat were named supporters of global terrorist groups for their activities in Afghanistan, Iraq and the Middle East. Along with Bank Sepah, which was already under U.S. and U.N. sanctions, the institutions account for more than 50 percent of Iran's banking sector, Treasury officials said.
"As awareness of Iran's deceptive behavior has grown, many banks around the world have decided as a matter of prudence and integrity that Iran's business is simply not worth the risk," Paulson said. "It is plain and simple: Reputable institutions do not want to be the bankers for this dangerous regime."
The sanctions also cover companies affiliated with the Revolutionary Guard Corps (IRGC) and the Ministry of Defense and Armed Forces Logistics (MODAFL), which were designated proliferators of ballistic missile technology. The Corps is the largest component of Iran's military. The defense ministry entity is the parent organization for Iran's aerospace and ballistic missile operations.
The Quds Force, a part of the Guard Corps that Washington accuses of providing weapons, including powerful bombs blamed for the deaths of U.S. soldiers in Iraq, was named a supporter of designated terrorist organizations.
The Revolutionary Guards organization, formed to safeguard Iran's 1979 Islamic revolution, has pushed well beyond its military roots, and now owns car factories and construction firms and operates newspaper groups and oil fields.
The sanctions also name several individuals: General Hosein Salimi, Commander of the Air Force, IRGC; Brigadier General Morteza Rezaie, Deputy Commander of the IRGC; Vice Admiral Ali Akhbar Ahmadian, Chief of the IRGC Joint Staff; Brigadier Gen. Mohammad Hejazi, Commander of Bassij resistance force; Brigadier General Qasem Soleimani, Commander of the Qods Force; Ahmad Vahid Dastjerdi, Head of the Aerospace Industry Organization (AIO); Reza-Gholi Esmaeli, Head of Trade & International Affairs Dept., AIO; and Bahmanyar Morteza Bahmanyar, Head of Finance & Budget Department, AIO.
The actions mean that any assets found in the United States belonging to the designated groups or individuals must be frozen. Americans are also forbidden from doing business with them.
Importantly, the designations also put companies outside the United States on notice that doing business with the designated groups could be a problem.
Now numbering about 125,000 members, they report directly to the supreme leader and officially handle internal security. The small Quds Force wing is thought to operate overseas, having helped to create the militant Hezbollah group in 1982 in Lebanon and to arm Bosnian Muslims during the Balkan wars.
The United States has long labeled Iran as a state supporter of terrorism and has been working for years to gain support for tougher sanctions from the international community aimed at keeping the country from developing nuclear weapons.
The sanctions being announced Thursday would be unilateral, however, and are believed to be the first of their type taken by the United States specifically against the armed forces of another government.
The sanctions reportedly will empower the United States to financially isolate a large part of Iran's military and anyone inside or outside Iran who does business with it.
Such steps could impact any number of foreign companies by pressuring them to stop doing business with the Revolutionary Guards or risk U.S. sanctions.
The administration also accuses the Quds Force of sending fighters and deadly roadside bombs, mortars and rockets to kill American troops in Iraq in recent years - allegations that Iran denies.
The United States pressures U.S. and European banks to do no business with Iranian banks, such as Bank Sedarat, that the Bush administration believes help finance guards' business operations. But the United States has been known for some time to also be considering naming the entire group as a foreign terrorist organization, allowing wider financial crackdowns.
The sanctions come several weeks after the U.S. Senate passed a resolution by Sens. Jon Kyl, R-Tex., and Joseph Lieberman, I-Conn., which called for naming Iran's Revolutionary Guard a "foreign terrorist organization" - which would mark the first time a sovereign nation's armed forces would be placed on the United States' terrorism blacklist. Critics suggested this could not only alienate Iranian citizens but also lead the administration to launch a military strike against Iran without a Declaration of War by Congress.
In a statement Thursday, Democratic presidential candidate Sen. Chris Dodd of Connecticut criticized the sanctions. "The aggressive actions taken today by the administration absent any corresponding diplomatic action is exactly what we all should have known was coming when we considered our vote on the Kyl-Lieberman Amendment, and smacks, frankly, of a dangerous step toward armed confrontation with Iran," Dodd said.
Speaking in Manchester, N.H., in his race for the Republican presidential nomination, Republican Mitt Romney said Thursday he would be willing to use a military blockade or "bombardment of some kind" to prevent Iran from gaining a nuclear weapon.
Other officials maintained the announcement is not a prelude to armed conflict with Iran despite concerns from some allies that the administration is building a case for war.
"In no way, shape or form does it anticipate the use of force," said Nicholas Burns, the State Department's No. 3 diplomat.
Nonetheless, CBS News chief White House correspondent Jim Axelrod reported that Defense Secretary Gates did acknowldge that there is planning for a military strike, planning that he calls "routine".