TEHRAN — The head of Iran’s elite Revolutionary Guards dismissed the possibility of an American military action against Iran and warned that his forces would respond with an “even more decisive” strike if attacked, an Iranian news agency reported today.

The comments by General Mohammad Ali Jafari came after America announced sweeping new sanctions against Iran focusing on the Revolutionary Guards, a force that is tasked with protecting Iran’s Islamic government and reports to the country’s supreme leader.

The sanctions step up tensions between America and Iran, where many fear Washington is planning military action. America accuses the Guards of supporting terrorism by backing Shiite militants in Iraq. Washington also accuses Tehran of seeking to develop nuclear weapons and has vowed to prevent it from doing so — though the Bush administration insists it is seeking diplomatic means. Iran denies trying to build weapons.

Asked about the possibility of an American strike on Iran, General Jafari told reporters late yesterday that, “These words are just exaggerations, and I don’t consider them a threat,” the news agency ISNA reported.

“The Islamic Republic has the strength and power of its people’s faith. This power is joined with experience, knowledge, and technology in the realms of defense. The enemy knows it cannot make any mistake, so these words are just exaggeration,” he said.

The sanctions ban American dealings with the extensive network of businesses believed linked to the Guards — and put stepped-up pressure on international banks to cut any ties with those firms.

A Foreign Ministry spokesman, Mohammad Ali Hosseini, dismissed the new American measures as “worthless and ineffective” and said they were “doomed to fail as before.”

Interior Minister Mostafa Pourmohammadi vowed that anyone who attacks Iran would “find itself faced with a hard and crushing response,” though he said the probability of American attack is “very small.”

“America knows well that while it can start such an attack, how it ends will not be in Washington’s hands, and such an attack will lead to America’s collapse,” he told journalists during a visit to Kuwait yesterday, according to the Iranian state news agency IRNA.

China, a key ally of Iran, warned today that the sanctions could increase tensions over Iran’s nuclear program.

“Dialogue and negotiations are the best approach to resolving the Iranian nuclear issue,” the ministry said in a brief statement. “To impose new sanctions on Iran at a time when international society and the Iranian authorities are working hard to find a solution to the Iranian nuclear issue can only complicate the issue.”

Foreign Minister Tzipi Livni of Israel was due to visit China over the weekend to lobby for intensified U.N. sanctions against Iran, the Israeli Embassy said today.

Washington has already won two U.N. Security Council sanctions resolutions.

Despite their government’s insistence that American and U.N. sanctions aren’t causing any pain, some leading Iranians have begun to say publicly that the pressure does hurt. And on Tehran’s streets, people are increasingly worried over the economic pinch.

Iran’s economy is struggling, with dramatic price rises this year. The cost of housing and basic foodstuffs like vegetables have doubled or even quadrupled. The government also has imposed unpopular fuel rationing in an attempt to reduce expensive subsidies for imported gasoline.

The sanctions have heightened resentment of America among some in the public. But they are also fueling criticism among Iranian politicians that President Ahmadinejad is mismanaging the crisis with hard-line stances that worsen the standoff with the West.

Mr. Ahmadinejad and his allies are likely counting on sanctions to rally Iranians against America.

“Hard-liners in Tehran were looking forward for the sanctions. It helps them hide their incompetence behind the embargo,” a political commentator, Saeed Laylaz, said.

But many conservatives who once backed Mr. Ahmadinejad have joined his critics. They point to his failure to fulfill promises to repair the economy — despite increased oil revenues — and say his fiery rhetoric goads the West into punishing Iran.

Mr. Ahmadinejad on Wednesday called earlier U.N. sanctions, which punish a list of Iranian companies believed linked to the nuclear program, “a pile of papers that have no value.”

Most notably, the new sanctions ban dealings with two major Iranian banks, Bank Melli and Bank Mellat, adding them to a list of already banned banks. That means the banks will have difficulty turning to European banks for dollars, a former Treasury Department terrorism expert now with the Washington Institute for Near East Policy, Matthew Levitt, said.