“We can’t let that happen.”
Israel has shared intelligence with the US suggesting the Islamic Republic was within weeks of producing a nuclear bomb.
Israel ‘doing well’
The president also said it was “very hard” to ask Israel to stop its strikes on Iran.
“I think it’s very hard to make that request right now,” Trump told reporters after stepping off Air Force One.
“If somebody is winning, it’s a little bit harder to do than if somebody is losing, but we’re ready, willing and able, and we’ve been speaking to Iran, and we’ll see what happens.”
Israel is “doing well in terms of war” and “Iran is doing less well”, he added.
Iran continued its strikes on Israel on Friday (local time) and successfully targeted the northern city of Haifa.
At least 19 people were injured when a missile evaded Israel’s air defences and slammed into an area by Haifa’s docks, blowing out windows and littering the nearby ground with rubble.
Israel’s military chief has warned of a “prolonged campaign” against Iran and that Israel was fighting a “multi-front war”.
On a visit to the Gaza Strip, Eyal Zamir said in a video statement to Israelis: “We have embarked on the most complex campaign in our history to remove a threat of such magnitude, against such an enemy. We must be ready for a prolonged campaign.”
Zamir said the Israeli military had prepared for “years” for the campaign against Iran, even while Israeli troops continue their devastating campaign against Hamas in Gaza.