Story highlights "There is a lot of internal discussion related to the 'why' on this," administration official says

We do believe that there were other targets," a State Department spokeswoman says

A Saudi prince says "someone in Iran" must "pay the price"

Iran summons a Swiss diplomat and lodges a complaint

Iran rejected allegations of an Iranian scheme to kill a Saudi Arabian ambassador, upbraiding on Wednesday a Swiss diplomat who represents American interests in Tehran and accusing the United States of fabricating the plot to deflect attention from its own pressing problems.

"Iran strongly denies the untrue and baseless allegations over a plan to assassinate the Saudi ambassador to Washington," Iranian Foreign Ministry spokesman Ramin Mehmanparast told the semi-official Iranian Students News Agency.

"The best method is disregarding such issues," Iranian Foreign Minister Ali Akbar Salehi told reporters on the sidelines of a Cabinet meeting Wednesday, according to the semi-official FARS News Agency. "Iran enjoys bilateral and good relations with Saudi Arabia and, if there is any difference, it is over international issues." He said the accusation was based on an Israeli-U.S. plot.

Tehran's responses came amid widespread outrage toward Iran from world leaders and the U.S. imposition of sanctions on an Iranian airline with ties to the government entity accused in the alleged plot.

Iran's Foreign Ministry summoned the Swiss charge d'affaires to answer questions about the U.S. allegations, Iran's semi-official Mehr news agency reported. The Swiss diplomat said he would inform the United States of the complaint. Switzerland represents U.S. interests in Iran because Iran and the United States don't have diplomatic relations.

Ali Larijani, Iran's speaker of parliament, railed against Washington.

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"The Americans acted unprofessionally in their childish play against Iran," he said. "The Americans want to divert attention from their own domestic problems as well as the awakening of the Muslim world by initiating a stupid mischief, which apparently is quite complicated."

Salehi called the alleged plot "an amateurish scenario" and told ISNA that similar allegations have arisen in the decades since the 1979 Islamic revolution.

"The Islamic Republic never seeks to get involved in this kind of behavior and, despite 32 years of pressure brought to bear on Iran, the country has always acted and reacted ethically," he said.

Salehi said the United States is trying to divert attention from its own "economic troubles."

But Saudi Prince Turki al-Faisal delivered tough words against Iran about the consequences of the alleged plot. "Someone in Iran is going to have to pay the price," he said.

Al-Faisal, a key member of the royal family, was speaking Wednesday at a conference in London. His representatives said the remark was his personal view and not the official Saudi position. The Royal Embassy of Saudi Arabia in Washington called the alleged plot "a despicable violation of international norms, standards and conventions" and said it "is not in accord with the principles of humanity."

U.S. Vice President Joe Biden, appearing on CBS, said "the consequences for Iran, I think, will be serious."

"I think what we have to do is unite the entire world against the Iranian behavior," he said.

Biden said the United States is laying out its case to world leaders about the alleged plot. He told NBC that there must be "accountability for Iran and further isolation of Iran in terms of their ability to operate around the world." Iran is already subject to numerous American sanctions.

"Every nation in the world, when they learn the facts of this, will be outraged that (Iran) would violate such an international norm, in addition to obviously being a crime to assassinate anybody, and in the process probably have killed scores of Americans," the vice president told NBC.

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U.S. Secretary of State Hillary Clinton said that "Iran must be held accountable for its actions." She said the United States is seeking international support to jack up the pressure on Iran. "This kind of reckless act undermines international norms and the international system," she said.

Clinton cited the punishment of Iranian individuals and institutions with sanctions. Her remarks were made as the Treasury Department announced the sanctioning of Mahan Air, an Iranian commercial airline.

It was cited for "providing financial, material and technological support" to the Islamic Revolutionary Guard Corps-Quds Force, the Iranian group linked to the alleged plot.

The airline flies Quds Force personnel between Iran and Syria for military training and facilitated their travel into and out of Iraq. It provides transportation services to Hezbollah, the Lebanese group regarded as a foreign terrorist organization, the department said.

"Mahan Air's close coordination with the IRGC-QF -- secretly ferrying operatives, weapons and funds on its flights -- reveals yet another facet of the IRGC's extensive infiltration of Iran's commercial sector to facilitate its support for terrorism," said the Treasury Department's undersecretary for terrorism and financial intelligence, David S. Cohen. "Following the revelation about the IRGC-QF's use of the international financial system to fund its murder-for-hire plot, today's action highlights further the undeniable risks of doing business with Iran."

President Barack Obama spoke Wednesday to King Abdullah of Saudi Arabia about the alleged plot, the White House said in a statement from the office of the press secretary.

"The president and the king agreed that this plot represents a flagrant violation of fundamental international norms, ethics, and law," the statement said. "They also praised the work of intelligence and law enforcement agencies that led to the disruption of this plot, and reiterated the joint commitment on the part of the United States and Saudi Arabia to pursue a strong and unified international response that holds those responsible accountable for their actions."

Senior members of the Obama administration debated Wednesday what they believe might have been the motivation behind the alleged plot. "There is a lot of internal discussion related to the 'why' on this," one official said.

After members of the Senate Armed Intelligence Committee were briefed by intelligence agencies, the State and Treasury Departments, Chairwoman Dianne Feinstein said there was no doubt that the Quds Force was involved, but she could not say if higher levels of government were too.

"I could surmise that the Quds Force would not have done this without the highest levels of approval from the Revolutionary Guard and, most likely, from some higher elements of the government," she said. But, she added, she could not specify who might have known.

She added that the alleged plot may have been just one in a series of such schemes. "It's hard for me to believe that there is just one plot involving the United States," she said. "I think we need to explore whether there are other plots going on in other countries."

Still, the Democrat from California said, "I'm not saying there is a broader plot; I'm just saying we need to look at that."

Vice Chairman Saxby Chambliss, R-Georgia, told reporters that the alleged plan was not directed at the United States and that military action against Iran is not warranted.

But a chorus of politicians called for some sort of U.S. reaction. "This kind of behavior by Iran cannot go un-responded to," said Sen. Joe Lieberman, I-Connecticut and chairman of the Homeland Security Committee, who predicted that the administration would announce new economic sanctions on Tehran.

"I don't think anything should be taken off the table at this point and time," said Senate Foreign Relations Committee Chairman John Kerry, D-Massachusetts.

House Armed Services Committee Chairman Carl Levin, D-Michigan, called the allegation "a very, very serious business, and we'll have a serious response." He said he had not seen the options the administration was considering.

House Speaker John Boehner, R-Ohio, told reporters Wednesday that the alleged plot is "a serious breach of international behavior" and called on the Obama administration to respond. "I would hope that our administration would hold the Iranian government -- hold their feet to the fire over the actions that have been alleged in this complaint," he said.

Deputy Secretary of State William Burns briefed U.S. diplomats Wednesday to explain how the alleged scheme evolved, how the Obama administration handled it, and the need to hold Iran accountable, a State Department official said.

On Tuesday, the Treasury Department sanctioned five individuals, four members of the IRGC-Quds Force and the alleged plot arranger, State Department spokeswoman Victoria Nuland told reporters. She said U.S. authorities believe the plans went beyond what has been made public.

"I would simply say that we do believe that there were other targets, and there were follow-on notions by these plotters, but we do believe that the entire plot has now been disrupted," she said.

The United States planned to contact leaders from the Arab League; the Gulf Cooperation Council, a coalition of Persian Gulf nations; and the Organization of the Islamic Conference, which is composed of 56 primarily Islamic states and promotes Muslim solidarity, said two Obama administration officials.

The State Department issued a worldwide travel alert about "the potential for anti-U.S. actions" in the wake of the thwarting of the alleged plot.

A spokesman for British Prime Minister David Cameron said Britain is consulting with the United States on further action against Iran. "We are in close touch with the U.S. authorities and we will support measures to hold Iran accountable for its actions," the spokesman said.

The French Foreign Ministry said the alleged plot is an "extremely serious affair, an outrageous violation of international law, and its perpetrators and backers must be held accountable."

Details about the case surfaced Tuesday.

Manssor Arbabsiar, a 56-year-old naturalized U.S. citizen, and Gholam Shakuri, an Iran-based member of Iran's Islamic Revolutionary Guard Corps, are accused of conspiracy to murder a foreign official, conspiracy to use a weapon of mass destruction, and conspiracy to commit an act of terrorism, the FBI said Tuesday.

Arbabsiar was arrested in September. David Tomscha, a friend of Arbabsiar in Corpus Christi, Texas, said the man traveled to Iran once a year and owns property in Iran.

Shakuri remains at large, the bureau said.

The two were in a group that began planning last spring to kill Saudi Ambassador Adel Al-Jubeir, the FBI said.

Robert Jordan, a former U.S. ambassador to Saudi Arabia, said Al-Jubeir "is so close to King Abdullah that I think it does make him a target to some degree. He is almost like a son to the king."

The Saudi ambassador was not the only intended target, U.S. officials said. The suspects also discussed attacking the Israeli and Saudi Embassies in Washington and possibly in Buenos Aires, a senior U.S. official said.

It is unclear why the Saudi ambassador may have been targeted, the official said, or how widespread knowledge or approval of the alleged plot may have been within Iranian President Mahmoud Ahmadinejad's government.

Authorities developed the case against the suspects with the help of an undercover informant posing as an associate of a Mexican drug cartel, according to officials and an FBI agent's affidavit released Tuesday.

Arbabsiar and the informant allegedly discussed using explosives to kill the ambassador, possibly in a crowded restaurant, according to the affidavit.

The informant named $1.5 million as his price, it said. Arbabsiar allegedly sent $100,000 intended as a down payment, telling the informant his "cousin" had deep pockets, court documents said.

A spokesman for Southern University in Baton Rouge, Louisiana, said Arbabsiar attended the school from the fall of 1983 until the following summer, graduating with a degree in mechanical engineering.

The alleged scheme involved the Quds Force, which is suspected of involvement in a number of international operations, court documents and U.S. officials said.

U.S. officials accuse the Quds Force of sponsoring attacks against U.S. and coalition forces in Iraq, the affidavit released Tuesday said. In October 2007, the Treasury Department designated it as "providing material support to the Taliban and other terrorist organizations."

Cooperation with the Mexican government played a key role in the investigation, U.S. officials said.The alleged scheme involved the Quds Force, which is suspected of involvement in a number of international operations, court documents and U.S. officials said.

U.S. officials accuse the Quds Force of sponsoring attacks against U.S. and coalition forces in Iraq, the affidavit released Tuesday said. In October 2007, the Treasury Department designated it as "providing material support to the Taliban and other terrorist organizations."

Cooperation with the Mexican government played a key role in the investigation, U.S. officials said.