US President Donald Trump said Sunday that the joint US-Israeli military campaign launched against Iran is expected to last around four weeks.

"It's always been a four-week process," Trump told the Daily Mail. "As strong as it is, it's a big country, it'll take four weeks — or less," he added.

Trump said he had not been surprised by any of the outcomes so far.

"I think it's going as per planned, other than we took out their entire leadership -- far, far more than what we thought," he said, reiterating his claim that 48 Iranian leaders had been eliminated.

On the possibility of Saudi Arabia joining the fight, he suggested that the Kingdom was already engaged.

"They're fighting, they're fighting too," he said, though there have been no public statements from Riyadh confirming this.

The remarks came after a CNN reporter in a since-deleted video shared by the news outlet said that Saudi Crown Prince Mohammed bin Salman had authorized the Kingdom to strike back at Iran if necessary, accusing Iran of targeting Saudi Arabia despite strikes against it not using Saudi airspace.

Trump also expressed hope that a democracy could emerge in Iran after the strikes conclude.

"A lot of very positive things could happen," he said.

'We intended four to five weeks'

Separately, Trump told the New York Times that the war could last up to “four to five weeks."

It “won’t be difficult” for Israel and the US to maintain the intensity of the battle, he said in an interview.

He insisted that the Pentagon retained plenty of forces, missiles and bombs to sustain the military assault “if we have to.”

“Well, we intended four to five weeks," he said, when asked how long the US and Israel could keep up the level of attacks.

“It won’t be difficult,” he stressed. “We have tremendous amounts of ammunition. You know, we have ammunition stored all over the world in different countries.”

Trump also said that he had “three very good choices” about who could lead Iran.

US forces struck Iranian command centers, ballistic missile sites, naval vessels and air defense systems in the opening 24 hours since the attacks began Saturday, deploying B-2 stealth bombers, fighter jets, nuclear-powered aircraft carriers and guided-missile destroyers, among other assets, according to the United States Central Command (CENTCOM).

Trump said earlier that 48 Iranian leaders had been eliminated and that operations were "ahead of schedule."

Iran has retaliated with drone and missile strikes targeting Gulf countries. Three US service members have been killed and five seriously wounded since operations began. (AA)

Update news