Sounds like it might be in the works:
A senior Western diplomat, speaking on condition of anonymity, told reporters that he expected the letter to be sent to Mr Khamenei before the Iranian elections this summer, although Washington's allies would prefer this step to be taken after the vote, to avoid influencing the election.
The last time reports about a letter to Iran circulated, the White House emphatically denied it.
But last week a State Department spokesman said he did not have anything to say about a letter, adding that he would not discuss the options being considered. He then referred reporters to the White House.