Donald Trump says he has told Iran it has to do "two things" to avoid military action, as the US builds up its forces in the Gulf.
"Number one, no nuclear. And number two, stop killing protesters," the US President said, adding that "they are killing them by the thousands".
"We have a lot of very big, very powerful ships sailing to Iran right now, and it would be great if we didn't have to use them."
His latest remarks follow weeks of pressure on Iran to negotiate a deal on its nuclear programme.
Iran's Foreign Minister Abbas Araghchi has said armed forces were ready "with their fingers on the trigger" to "immediately and powerfully respond" to any aggression.
