Trump also said he would state in the address, which is due at 9pm EDT on Wednesday (noon AEDT on Thursday), that he was considering withdrawing the United States from the NATO military alliance.
Asked when the US would consider the Iran war over, Trump said: "I can't tell you exactly ... we're going to be out pretty quickly."
He was expected to reiterate a two-to-three-week timetable for ending the war in Iran during the address, a White House official later said.
US action had ensured Iran would not have nuclear arms, Trump said: "They won't have a nuclear weapon because they are incapable of that now, and then I'll leave, and I'll take everybody with me, and if we have to we'll come back to do spot hits."
An Iranian official, Mehdi Tabatabai, said in a post on X that an important letter to the US public from Iran's President Masoud Pezeshkian would be released "in a few hours".
Global oil supplies were expected to be hit twice as hard this month as in March, the International Energy Agency said on Wednesday, underlining the urgent need for an end to the conflict Trump began with Israel on February 28.
Trump said separately on social media that Iran had asked for a ceasefire but that he would not consider it until it ceased blocking the Strait of Hormuz, a major fuel shipment route.
Iran denied making any such request.
Two security sources from Pakistan, which is mediating in the conflict, earlier told Reuters that Pakistani officials had proposed a temporary ceasefire to both sides but had not heard back from either.
US Vice President JD Vance communicated with intermediaries from Pakistan about the Iran conflict as recently as Tuesday, a source briefed on the matter told Reuters on Wednesday.
At Trump's direction, Vance signalled privately that Trump was open to a ceasefire as long as certain US demands were met, including reopening the Strait of Hormuz, the source said.
Trump had signalled on Tuesday he could wind down the war in two to three weeks even without a deal, and scaled up threats to pull the US out of NATO if European countries did not help stop Iran threatening the waterway.
In his remarks to Reuters on Wednesday, Trump said he would express his disgust with NATO for what he considers the military alliance's lack of support for US objectives in Iran.
European countries took pains to appear unruffled and France's junior army minister Alice Rufo said operations by NATO in the Strait of Hormuz would be a breach of international law.
The conflict has killed thousands, spread across the region and caused unprecedented energy disruption.
IEA head Fatih Birol said the main issue so far from Iran's effective closure of the Strait of Hormuz was the lack of jet fuel and diesel that was already a problem in Asia and would hit Europe in April or May.
Drones hit fuel tanks at Kuwait's international airport, causing a big blaze, and authorities in Bahrain reported a fire at an undisclosed company facility from an Iranian attack.
Qatar said an oil tanker leased to state-owned QatarEnergy was hit by an Iranian cruise missile in Qatari waters but that there were no injuries or environmental damage.
An overnight strike hit Shahid Haghani Port, Iran's largest passenger terminal, deputy regional governor Ahmad Nafisi told state media, calling it a "criminal" attack on civilian infrastructure.
In Tel Aviv on Wednesday, evening air raid sirens and air defence systems were repeatedly triggered as Iran fired a volley of missiles about an hour before the start of Passover, the Jewish festival of freedom.
Israel's fire and rescue service said there had been multiple "impacts" in the greater Tel Aviv area.
Shortly after the latest Iranian attack, the Israeli military said in a statement that the air force was carrying out strikes on dozens of targets across Tehran.
with AP
