US President Donald Trump briefly laid out his case for a possible attack on Iran in his State of the Union speech to Congress on Tuesday, saying he would not allow the world’s biggest sponsor of terrorism to have a nuclear weapon.

Even while assembling a massive military force in the Middle East, Trump has done little to explain to the American public why he might be leading the US into its most aggressive action against the Islamic Republic since its 1979 revolution.

In his speech, Trump pointed to Tehran’s support for militant groups, its killing of protesters and the country’s missile and nuclear programs as threats to the region and the United States.

“The (Iranian) regime and its murderous proxies have spread nothing but terrorism and death and hate,” the Republican president said about 90 minutes into his annual address to a joint session of the Senate and House of Representatives.

He accused Iran of restarting its nuclear program, working to build missiles that “soon” would be capable of reaching the United States and of being responsible for roadside bombings that have killed US service members and civilians.

Iranian state media have claimed that Tehran is developing a missile capable of reaching North America.

The run-up to Trump’s address was overshadowed by the buildup of US military forces in the Middle East and preparations for a possible conflict with Iran that could last for weeks if Tehran does not reach a deal to solve a longstanding dispute over its nuclear program.

Trump has repeatedly expressed frustration with negotiators’ failure to reach an agreement. “They want to make a deal, but we haven't heard those secret words, ‘We will never have a nuclear weapon,’” Trump said in his speech.

Iran says its nuclear research is for civilian energy production.

Trump also faulted the government in Tehran for the deaths of thousands of protesters during recent anti-government demonstrations, although the specific figure he cited - that 32,000 people had been killed - is much higher than most public estimates.

“What is claimed about Iran’s nuclear program, Iran’s intercontinental ballistic missile, and the number of people killed in the January unrest is nothing but the repetition of a series of big lies,” Iran’s foreign ministry spokesperson Esmaeil Baghaei said in a post on X on Wednesday.

‘Forever Wars’

Secretary of State Marco Rubio held a briefing on Iran hours before the speech for Congress’ “Gang of Eight” - composed of the leaders of the Senate and House of Representatives and the two chambers’ intelligence committees.

“First and foremost, if they want to do something in Iran - and who the hell knows what it is - they should make it public and discuss it with the public and not keep it in secret. When you do these military operations in secret, it always causes longer wars, tragedy, more expenses and mistake(s),” Senate Democratic Leader Chuck Schumer told a press conference shortly before the classified session.

Advisers had urged Trump to focus on the economy, immigration and other domestic policy issues, and he devoted the lion's share of his nearly two-hour-long speech to such topics.

Trump and his fellow Republicans rose to the top of US politics with the passionate support of a political base that embraces his “America First” policies and vows to end an era of “forever wars” like the long conflicts in Iraq and Afghanistan.

But opinion polls show the party will struggle to keep control of Congress in November’s midterm election.

Polls also show Americans wary of foreign conflicts. A Reuters/Ipsos poll from January showed 69% of Americans agreed with a statement that the US should only use its military when facing a direct and imminent threat, while 18% disagreed and the rest weren’t sure or didn’t answer the question.

Trump ordered strikes on Iran last year, claiming in July that they had “obliterated” the country’s nuclear facilities. His aides have claimed more recently that Iran is very close to having the ability to make nuclear bombs.

Trump addressed the issue in Tuesday’s speech, saying, “They (Iran’s leaders) want to start all over again, and are, at this moment again pursuing their sinister ambitions.”

Trump said he preferred to make peace, listing a range of worldwide conflicts he takes credit for ending, or easing.

“As president, I will make peace wherever I can, but I will never hesitate to confront threats to America wherever we must,” Trump said.