The official said Sunday that the U.S. 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 U.S. 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 U.S. federal prosecutors that an Iranian government agent was involved in plotting the assassination of the Saudi ambassador.