The United States announced on Tuesday that it has received a letter from Iran over its allegations of an Iranian plot to murder the Saudi ambassador in Washington.\"We did receive a lengthy diplomatic note from the Swiss protecting power on behalf of the Iranians,\" US State Department spokeswoman Victoria Nuland said after Washington received the letter from Swiss intermediaries. In the absence of US-Iranian diplomatic relations for more than three decades, Switzerland acts on behalf of US interests in Tehran. \"It was about seven pages. It was a rant. It was full of all kinds of denials. There was not a lot new in there from our perspective,\" Nuland told reporters. In Tehran, Iranian Foreign Ministry Spokesman Ramin Mehman-Parast said Tuesday that Iran had sent a letter to the United States seeking an \"official apology of the Americans in protest at this made-up scenario\". He explained the Iranian letter was in response to a US one, whose contents he did not divulge. On October 11, US officials alleged Iran\'s Quds Force of the Islamic Revolution Guards Corps (IRGC) 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. Iran has strongly denied involvement, describing the allegations as \"baseless scenario\". Tehran said the claim meant to tarnish its \"good relations\" with Saudi Arabia and also distract the world attention from anti-capitalism protests in the US.