Trump's comments came as the conflict expanded on its fifth day, with a US submarine sinking an Iranian warship off the coast of Sri Lanka and fresh blasts across the Middle East.

"We're doing well on the war front, to put it mildly. Somebody said on a scale of 10, where would you rate it? I said about a 15," Trump told a gathering of tech bosses at the White House.

"We're in a very strong position now, and their leadership is just rapidly going. Everybody that seems to want to be a leader, they end up dead."

Trump added that Tehran's arsenal of ballistic missiles was being "wiped out rapidly."

He repeated his justifications for attacking Iran, saying Tehran was on its way to obtaining a nuclear weapon.

"When crazy people have nuclear weapons, bad things happen," Trump added.

The US leader pledged that he would "continue forward" with the joint air campaign with Israel that has already slain Iranian supreme leader Ali Khamenei on its opening day on Saturday.

Trump's administration has faced criticism after days of mixed messages about the rationale for the war, given the Republican's previous campaign boasts about starting "no new wars."

- 'Paying in blood' -

He has yet to spell out his plan for what happens after the war or to say whether he wants a wholesale change in Iran's government, or to work with remnants who would deal with Washington.

Trump has pursued a policy of working with figures from the Venezuelan government following the US toppling of Nicolas Maduro in January -- and making a deal to extract Venezuelan oil.

The White House said Wednesday that Iran's clerical government was being "absolutely crushed" and was "paying in blood" -- but declined to confirm Trump wanted regime change in Tehran.

But Trump is "actively considering" a US role in Iran after the American-Israeli operation against the country concludes, White House Press Secretary Karoline Leavitt said.

"I think it's something the president is actively considering and discussing with his advisors and his national security team," Leavitt told a briefing.

Leavitt also rejected as "false" reports that Trump had agreed to arm Kurdish separatist militia in Iran so that they could rise up against the government.

But she confirmed that Trump had spoken to Kurdish leaders. The Wall Street Journal reported Trump was considering supporting Kurdish groups.

Leavitt also said the United States and Israel expected to "complete and total dominance" over Iranian airspace in the "coming hours", echoing comments made earlier by the Pentagon.