Iran has vigorously rejected US allegations that it had backed a plot to kill the Saudi ambassador to Washington, with a senior official describing them as a "childish, amateur game".
Ali Larijani, the parliament speaker, said on Wednesday that the "fabricated allegations" aimed to divert attention from Arab uprisings that Iran says are inspired by its own Islamic revolution that toppled the Shah in 1979.
The primary evidence linking Iran to the alleged conspiracy is that the arrested suspect is said to have told US law-enforcement agents that he had been recruited and directed by men he understood were senior Quds Force officials.
The Quds Force is an unit of the Iranian Revolutionary Guards.
"America wants to divert attention from problems it faces in the Middle East, but the Americans cannot stop the wave of Islamic awakening by using such excuses," Larijani said during an open session of Iran's parliament.
"These claims are vulgar. We believe that our neighbours in the region are very well aware that America is using this story to ruin our relationship with Saudi Arabia."
But Saudi Arabia strongly condemned the alleged plan to kills its ambassador, the SPA state news agency reported, quoting an unnamed official.
"The Kingdom strongly condemns the sinful and abhorrent attempt to assassinate the [Saudi] envoy... to the Unites States," SPA said, quoting the official.
Hillary Clinton, the US secretary of state, said that Iran's alleged ties to a the plot marked a "dangerous escalation of the Iranian government's long-standing use of political violence and sponsorship of terrorism".
Sanctions against Iranian airline
In another development, the US Treasury Department slapped sanctions on Iran's Mahan Air on Wednesday, saying it had secretly transported members of the Quds Force.
The department said the commercial carrier had transported members of the unit and Hezbollah across the Middle East.
Any of the airline's assets in the US will now be frozen and US citizens will be barred from doing business with the firm.
The secretary general of the Gulf Co-operation Council condemned the alleged plot, saying it would severely harm relations.
Abdulattif al-Zayani said in a statement he considered the plot a "flagrant violation" of all laws and international agreements.
Earlier, Iran's ambassador to UN voiced outrage and complained of politically motivated "war-mongering" by the US.
"The Iranian nation seeks a world free from terrorism and considers the current US war-mongering and propaganda machine against Iran as a threat not just against itself but to the peace and stability in the Persian Gulf region," Mohammad Khazaee said in a letter to Ban Ki-moon, the UN chief.
|Mohammad Marandi, an Iranian political analyst, discusses the US accusations
However, Prince Turki al-Faisal, a former Saudi intelligence services chief, said the evidence that Iran was behind a plot was overwhelming.
"The burden of proof is overwhelming ... and clearly shows official Iranian responsibility for this," he said on Wednesday.
"Somebody in Iran will have to pay the price."
Saudi-Iranian tensions have increased since March, when Saudi Arabia, which sees itself as the bastion of Sunni Islam, sent troops to help Bahrain's Sunni rulers quell pro-democracy protesters led by the island's Shia majority.
Bahrain accuses Iran of being behind the unrest, a charge denied by Tehran and by Bahraini Shia political parties.
Britain, for its part, said it would support "measures to hold Iran accountable for its actions".
A spokesman for David Cameron, the UK prime minister, described the alleged Iranian involvement in the plot as "shocking".
Eric Holder, the US attorney general, said on Tuesday that factions within the Iranian government were involved in the plot.
He said the plot was "conceived, sponsored and directed from Iran".
Criminal charges filed
The US has filed criminal charges against Manssor Arbabsiar, a 56-year-old naturalised US citizen holding both Iranian and US passports, and Gholam Shakuri, an Iran-based member of Quds Force, the justice department said.
A federal criminal complaint in New York said the two are also charged with conspiring to use a weapon of mass destruction.
It said the Saudi ambassador, Adel al-Jubeir, was in the US when the death plot was supposed to have been carried out.
|Arbabsiar was arrested on September 29 at New York's JFK International Airport [Reuters]
Shakuri remains at large, while Arbabsiar was arrested on September 29 at New York's John F Kennedy International Airport.
The case, called Operation Red Coalition, began in May when an Iranian-American from Corpus Christi, Texas, approached a US informant seeking the help of a Mexican drug cartel to assassinate the Saudi ambassador, according to counter-terrorism officials.
The Iranian-American thought he was dealing with a member of a Mexican drug organisation, according to documents.
The Mexican embassy in Washington issued a statement suggesting the two countries co-operated closely.
"From the very first moment, Mexico and the US exchanged information and acted in a co-ordinated way," the embassy said.