President Donald Trump met his National Security Council on Tuesday to discuss the Iran-Israel war, the White House said, as the US leader considered whether to join Israel's air campaign against Tehran.

The meeting in the White House Situation Room lasted around one hour and 20 minutes, a White House official said on condition of anonymity, without giving more details.

The meeting comes after Trump said the United States would not kill Iran's supreme leader "for now" and demanded Tehran's "unconditional" surrender, as US ally Israel traded fire with its arch foe for a fifth day.

US officials said Trump was keeping all all options on the table, while insisting that Washington had no hand in the campaign so far.

The most likely option under consideration by Trump would be the use of giant US "bunker-buster" bombs against Iran's deeply buried Fordow nuclear facility that Israel's bombs cannot reach.

The New York Times said Trump was also considering allowing US tanker aircraft to refuel Israeli combat jets so they could carry out long range missions. 

US officials said dismantling Iran's nuclear program — which Western countries say Tehran is using to seek a nuclear weapon, although the Iranian government denies this — remained Trump's priority.

But Trump's earlier comments implied that the assassination of Ayatollah Ali Khamenei is back on the table, just days after a US official said he had waved off such a move by Israel.