How Trump used 9/11 to make the case for a war with Iran

US President Donald Trump has used a memorial ceremony marking the 25th anniversary of 9/11 to draw a direct line between the "War on Terror" that followed the terrorist attacks and the on-going US-Israeli war on Iran.

In an unusual move, Trump paid his respects at the Pentagon rather than attending the main ceremony in New York, where two hijacked planes struck the Twin Towers at the World Trade Centre in a series of attacks that killed 2,977 people September 11, 2001.

He also touched on election conspiracy claims and a controversial midterm proposal, as Trump's approval rating sits near historic lows just two months out from the elections.

In his Pentagon address, Trump drew parallels between the September 11 attack and the US' deeply unpopular war in Iran.

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"Today we renew the sacred oath that we first swore in their names a quarter of a century ago. We will never, ever forget," Trump said. "That’s why we fight today."

"We don’t have a choice. There can only be victory. We fight hard. We fight to win."

He drew links between the fight against Al-Qaeda — launched by his Republican predecessor George W. Bush after the attacks — and the ongoing US-Israeli war against Iran, now in its seventh month.

"Today we salute every member of the United States military who served in the 'war on terror'," he said.

"And we salute the service members working right now to ensure the world’s number one sponsor of terror, the Islamic Republic of Iran, will never ever have a nuclear weapon."

US Defense Secretary Pete Hegseth used his own remarks at the ceremony to boast about the US' success in the war.

"Over the past six months, we have laid waste to the world's most prolific state sponsor of terrorism. Our warriors have fought an Islamic theocracy that has wished us death for nearly half a century," Hegseth said.

“We’re still sending terrorists where they belong, to hell, and tankers to the bottom of the ocean where they belong. And we’re ensuring that Iran will never have a nuclear weapon."

Hegseth claimed the US had destroyed Iran's defences and controlled the Strait of Hormuz, adding that "economic pressure tightens every day" and the US "will finish this fight".