US President Donald Trump said on Thursday that he would not use a nuclear weapon in the war against Iran.

"Why would I use a nuclear weapon? We've totally, in a very conventional way, decimated them without it," Trump told reporters at the White House when asked whether he would use such a weapon.

"No, I wouldn't use it. A nuclear weapon should never be allowed to be used by anybody," he added.

Asked how long he was willing to wait for a long-term peace deal with Iran, Trump said, "Don't rush me."

He said Iran might have loaded up their weaponry "a little bit" during the two-week ceasefire, but added that the US military could knock that out in about one day. "Their navy is gone. Their air force is gone, their anti-aircraft is gone ...maybe they loaded up a little bit during the two-week hiatus, but we'll knock that out about one day, if they did," Trump added.

Trump uses nuclear holocaust imagery

"I think there would be nothing worse than having a nuclear holocaust in Europe; London, Paris, various places in Germany, all targeted," he said.

Prime Minister Benjamin Netanyahu made comments on Iran's nuclear threat over recent weeks, stating that if the US and Israel did not conduct strikes on Iran as part of operations Rising Lion, Epic Fury, and Roaring Lion, then the names of Iranian nuclear facilities would be remembered in the same breath as the Nazi's concentration camps from the Holocaust.

"I want to make the best deal. I could make a deal right now ... but I don't want to do that. I want to have it everlasting," Trump said.