An Iranian-American man who US officials say has links to Iran's security forces pleaded not guilty in federal court on Monday to plotting to kill the Saudi Arabian ambassador to Washington in a bomb attack.

Manssor Arbabsiar, 56, who was arrested on September 29 in New York, faces several charges including conspiracy to murder a foreign official, conspiracy to use a weapon of mass destruction and conspiracy to commit an act of terrorism.

Another man, Gholam Shakuri, was also charged in the plot but is believed to still be in Iran. US officials said he is a member of Iran's Quds Force, the covert operations arm of the country's powerful Islamic Revolutionary Guard Corps.   

US prosecutors accused the two men of planning to assassinate the Saudi ambassador to the United States, Adel al-Jubeir, by planting a bomb in a Washington restaurant. The Iranian government denies any involvement.   

But details such as Arbabsiar's bumbling nature and his trust of a US federal informant impersonating a Mexican drug cartel figure, have raised eyebrows among Iran specialists as to the seriousness of the plot.

The consensus view in US President Barack Obama's administration is that Iran's supreme leader, Ayatollah Ali Khamanei, probably knew of the alleged plot to kill the Saudi ambassador, while President Mahmoud Ahmadinejad did not.

Ahmadinejad has said Washington had fabricated the plot to cause a rift between Tehran and Saudi Arabia and dominate the Gulf. - Reuters