United States President Donald Trump has issued a fresh warning to Iran, saying the country is running out of time.

In a post on Truth Social, Trump declared that Iran must act, warning that there would be nothing left of the country if it fails to do so.

The U.S. leader had earlier signaled his willingness to accept a 20-year suspension of Tehran's nuclear program in place of a complete halt.

"They fully agreed no nuclear and if they have any nuclear of any form, I don't read the rest of the 20 years is not enough for you. It's got to be a No, 20 years is enough. But the level of guarantee from them is uh in other words, it's got to be a real 20 years," Trump said.