The US Navy said it has not lost any drones over the Gulf recently, Reuters has reported.
Iran's media earlier said a US drone was captured by the naval unit of the Islamic Revolutionary Guards Corps in the last few days after flying into Iranian airspace.
More top news
Some 66 people have been killed after the plane they were travelling on crashed in southern Iran.
The letter calls for an end to harassment, abuse, and impunity in a world "ripe for change".
Police say that anyone who sees Whitehouse should not approach him, but instead call them on 999 and quote incident 23 of 18 February.