Iran has sent a letter to the United States seeking an "apology" overallegations of an Iranian assassination plot on US soil, foreign ministry spokesman Ramin Mehmanparast said Tuesday.

"A letter has been sent... It is our right to seek the official apology of the Americans in protest of this made-up scenario as these allegations are not true at all," Mehmanparast told a news conference, quoted by the official IRNA news agency.

He explained the Iranian letter was in response to a US one, whose contents he did not divulge.

Mehmanparast did not give details on how the letters were transmitted. Iran and the United States have had no direct diplomatic channels for more than three decades.

On October 11, US officials alleged Iran's Quds Force -- an elite wing of the Revolutionary Guards -- plotted to kill the Saudi ambassador to Washington by hiring assassins from a Mexican drug cartel for $1.5 million.

An Iranian-American car salesman accused of involvement in the plot pleaded not guilty in a New York court last week.

Iranian officials and leaders have fiercely denied any involvement in the alleged plot, calling it an attempt by Washington to divert attention from domestic economic woes and foreign policy failures in the Middle East.

The US and Iran broke off diplomatic ties after radical students in Tehran took US diplomats hostage following Iran's 1979 Islamic revolution.