Washington: An American official says Iran has formally complained to the US over claims the Iranian government was involved in an alleged plot to kill Saudi Arabia's ambassador to the United States.

The official said on Sunday that the US received a diplomatic note on Friday expressing displeasure with the charges that were leveled earlier this month.

Iran has already denied the allegations. The official said the note was delivered through the Swiss embassy in Tehran, which represents US interests in Iran since the two countries don't have diplomatic relations.

The official spoke on condition of anonymity to discuss a private diplomatic exchange.

Iran has angrily denied charges brought by US federal prosecutors that an Iranian government agent was involved in plotting the assassination of the Saudi ambassador.