US President Donald Trump threatened to launch another attack on Iran if Tehran attempts to rebuild its ballistic missile programme, warning he would act "immediately" against nuclear development during a meeting with Israeli Prime Minister Benjamin Netanyahu on December 29, a pool video recording showed him as saying.

"I hear that Iran is trying to build up again, and if they are, we're going to have to knock them down," Trump stated ahead of the meeting. "We'll knock them down. We'll knock the hell out of them."

Trump stated he would support an attack on Iran "immediately" if it attempts to redevelop nuclear capability, advising Tehran to instead seek a deal with Washington.

The American president went on to say that the Iranian economy was severely damaged by inflation and a weakened economy, and that an offer for talks was still on the table. 

"That's smarter. They could have made a deal the last time before we went through, you know, a big attack on them."

When asked whether the US would back an Israeli attack targeting Iran's missile programme, Trump stated: "If they will continue with the missiles, yes; the nuclear, fast. Okay, one will be yes, absolutely. The other is: We'll do it immediately."

The US bombed three Iranian nuclear facilities in June following Israeli strikes on June 13 that targeted nuclear facilities, senior military figures and scientists. Iran responded with missile attacks, including on a US base in Qatar, which did not result in American casualties.

Trump has repeatedly claimed the June strikes "obliterated" Iran's nuclear programme. However, Israeli officials warned in recent weeks that Iran is expanding its ballistic missile programme, with Netanyahu expected to make the case that more action could be required.

Tel Aviv believes Iran is rebuilding facilities linked to ballistic missile production and repairing air defences damaged in earlier strikes, viewing this as more urgent than nuclear enrichment efforts.

Israeli intelligence estimates Iran retained approximately 1,500 missiles following the 12-day war in June, down from 3,000 previously, with 200 launchers out of 400. Israeli sources stated Iran has begun taking steps to rebuild forces but has not returned to pre-war levels.

Senator Lindsey Graham, an Iran hawk close to Trump, visited Israel this month and repeated talking points about the dangers of Iran's long-range missiles.

Iran fired hundreds of missiles at Israel in June in response to the Israeli attack that killed the country's top generals, several nuclear scientists and hundreds of civilians.

Iran has ruled out negotiating over its missile programme, which forms the core of its defence strategy. "If they want to make a deal, that's much smarter," Trump stated on December 29.

On Gaza, Trump stated he will attempt to advance the second phase of the Gaza peace plan "as quickly as we can" ahead of his meeting with Israeli Prime Minister Benjamin Netanyahu on December 29,.

"Very quickly, as quickly as we can, but there has to be a disarmament, we have to disarm with Hamas," Trump told CNN's Kevin Liptak outside Mar-a-Lago in West Palm Beach, Florida.

More than two months after Trump travelled to Egypt to sign the Gaza peace agreement, crucial pieces of the deal remain undefined as Israel tightens its military grip on the battered enclave.

The second phase of the deal includes Hamas disarmament, the beginning of reconstruction and establishment of post-war governance. At the centre of the new plan for administering Gaza is creation of a "Board of Peace" to be led by Trump and other world leaders.

Pressed by reporters when reconstruction in Gaza could begin, Trump suggested it is "going to begin pretty soon".