US allegations that Iran plotted to assassinate Saudi Arabia's ambassador to Washington are a "mischievous" attempt to fuel tension between Tehran and Riyadh, a senior Iranian official said on Wednesday.
US authorities said on Tuesday they had broken up a plot by two men linked to Iran's security agencies to kill the Saudi envoy, Adel al-Jubeir. One man was arrested last month while the other was believed to be in Iran.
"These claims are vulgar ... It is a childish and amateur game," parliament speaker Ali Larijani told parliament in a speech broadcast live on state radio.
"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."
Foreign Minister Ali Akbar Salehi dismissed the allegations, saying the United States would have to apologise for its words.
"US allegations are mischievous and I assure you they will apologise in the future," Salehi was quoted as saying by Iran's Arabic-language television network Al Alam.
In London, a former chief of Saudi intelligence services said evidence that Iran was behind a plot to kill the Saudi Arabian ambassador to Washington was overwhelming.
"The burden of proof is overwhelming ... and clearly shows official Iranian responsibility for this. Somebody in Iran will have to pay the price," Saudi Prince Turki al-Faisal said.
Saudi-Iranian tensions have increased since March, when Saudi Arabia sent troops to help Bahrain's Sunni rulers quell pro-democracy protesters led by the island's Shi'ite majority, which has long complained of sectarian discrimination.
Bahrain accused Iran of being behind the unrest, a charge denied by Tehran and by Bahraini Shi'ite political parties.
US President Barack Obama called the alleged assassination plot a "flagrant violation of US and international law" and Saudi Arabia said it was "despicable".
Hasan Qashqavi, Iran's deputy foreign minister, ruled out any rupture of relations between Iran and Saudi Arabia, saying: "Such baseless allegations cannot have the least impact on our ties", the semi-official Fars news agency reported.
But some Iranian analysts disagreed.
"It will harm the ties (with Saudi Arabia) ... and in 2012 Tehran and Washington might even have a military confrontation," said analyst Saeed Leylaz.
The United States and Israel have not ruled out military action to prevent Iran from obtaining nuclear weapons. Tehran says its nuclear programme is strictly for peaceful purposes.
Saudi Arabia has indirectly accused Iran of stirring strife in its oil-rich Eastern Province, home to much of the kingdom's Shi'ite minority and the scene of protests earlier this year.
Larijani said Washington's "fabricated allegations" were aimed at diverting attention from popular uprisings in the Middle East, which Iran says were inspired by its own 1979 Islamic revolution that toppled the US-backed Shah.
"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.