The United States accused Iran on Tuesday of backing a plot to kill the Saudi ambassador to Washington, AFP reported.
American officials said they scuttled a plot by two men linked to Iran's security agencies to assassinate Saudi Ambassador Adel Al Jubeir in Washington.
One was arrested last month and is being held without bail in New York. The other is believed to be in Iran.
Court documents identified the two alleged plotters as Gholam Shakuri, who is a member of the Quds force, and Mansour Arbabsiar, who was arrested on September 29 when he arrived at John F. Kennedy International Airport from Mexico.
Arbabsiar, 56, who is a naturalized US citizen and holds an Iranian passport, initially cooperated with authorities after being arrested. He made calls to Shakuri after being arrested and acted as if the plot was still a go, court documents said.
Arbabsiar appeared briefly in a Manhattan courtroom on Tuesday, where he was ordered detained and assigned a public defender.
President Barack Obama called the plot a "flagrant violation of US and international law" and Saudi Arabia said it was "despicable."
Iran denied the charges and expressed 'outrage' at the allegation, which comes amid rising tensions between Tehran and Riyadh over recent events in the Persian Gulf.
Secretary of State Hillary Clinton, in a Reuters interview, expressed hope the countries that have hesitated to enforce existing sanctions on Iran would now "go the extra mile."
At a news conference, FBI Director Robert Mueller said the plot, which involved monitored international calls, Mexican drug money and an attempt to blow up the ambassador in a Washington restaurant, was reminicent of a Hollywood movie.
US Attorney General Eric Holder alleged that the plot was the work of the Islamic Revolutionary Guard Corps (IRGC) and its covert arm, the Quds force.
"High-up officials in those (Iranian) agencies, which is an integral part of the Iranian government, were responsible for this plot," Holder told the news conference. "I think one has to be concerned about the chilling nature of what the Iranian government attempted to do here," he said.
The primary evidence linking the Iranian government to the plot on Al Jubeir's life is the confession of one of the alleged conspirators, who told US law enforcement agents after his arrest he had been recruited and directed by men he understood were senior officials in the Quds force.
"It looks like it's the Quds Force, the IRGC," Senate Intelligence Committee Chairwoman Dianne Feinstein told CNN. "We do not know that it went up above the IRGC"
Feinstein added, "I just don't see how this could be done any other way, that even the Quds force would go out and do something on their own to assassinate somebody who represented a country, not even in that country but in a third country."
Officials said the Saudi ambassador, Al Jubeir, who is close to King Abdullah Bin Abdul Aziz and has been in his post since 2007, was never in danger.
The US State Department on Tuesday issued a worldwide travel alert for US citizens, warning of the potential for anti-US action resulting from Washington's allegations against Tehran.