Marco Rubio delivered a rare briefing to top US lawmakers on Iran, just a few hours before Donald Trump used his State of the Union address to say that Tehran would never be allowed to develop nuclear weapons.

Amid the largest deployment of aircraft and warships to the Middle East since the 2003 buildup to the Iraq war, Trump said he wanted to solve the confrontation with Iran through diplomatic means while claiming that Tehran was seeking to develop ballistic missiles that could reach the US, without providing further details.

“They’ve already developed missiles that can threaten Europe and our bases overseas,” he said. “And they’re working to build missiles that will soon reach the United States of America.”

“We are in negotiations with them,” he continued. “They want to make a deal. But we haven’t heard those secret words: we will never have a nuclear weapon.”

Rubio, the US secretary of state, delivered a classified briefing to the so-called “gang of eight”, which includes the senior lawmakers from both parties in the House and Senate, as well as the chairs and ranking members of the House and Senate intelligence committees.

The select group is briefed by the White House on classified intelligence matters, which can include preparations for significant military action. Rubio last publicly briefed the group on 5 January, the day after the US launched its successful operation to capture Venezuela’s Nicolás Maduro.

The developments came after a second US aircraft carrier, the USS Gerald Ford – the largest such vessel in the world – arrived in the region. Analysts have said that the US is now in position to launch a strike against Iran if Donald Trump orders one.

The details of the report were classified and were not immediately made public. Exiting the briefing, Senate minority leader Chuck Schumer said: “This is serious, and the administration has to make its case to the American people.”

“I’m very concerned,” said Jim Himes, the ranking democrat on the House intelligence committee. “Wars in the Middle East don’t go well for presidents, for the country, and we have not heard articulated a single good reason for why now is the moment to launch yet another war in the Middle East.”

The briefing by Rubio took place just hours before Trump was scheduled to deliver a State of the Union speech on Tuesday evening in which his foreign policy was expected to play a central role. Trump has demanded that Iran abandon its nuclear programme, abandon its production of ballistic missiles and cease its support for overseas proxies such as Hezbollah and the Houthis in Yemen.

US-Iran talks are scheduled for Thursday in Geneva. In an interview with NPR, the deputy foreign minister, Majid Takht-Ravanchi, said that Iran was “ready to reach an agreement as soon as possible”.

“We want to do whatever’s necessary to make it happen,” he continued. But the negotiations would only concern Iran’s nuclear programme, he added, which is unlikely to satisfy the White House.

Trump last week said that Iran would either make a deal or the US would have to “take it a step further”, adding that “really bad things” would happen to Iran, adding a time limit of 10 days.

The US has also evacuated non-essential personnel from its embassy in Lebanon due to an assessment of the “threat environment”, and Rubio has also reportedly delayed a Saturday meeting with Israel’s Benjamin Netanyahu to Monday, according to Israeli officials.

The Guardian and other media outlets have reported that Gen Dan Caine, the chair of the joint chiefs of staff, had warned Trump that a conflict with Iran could severely deplete the US’s stockpile of anti-missile missiles including Patriot, Terminal High Altitude Area Defense (THAAD) and ship-launched interceptors.

Trump had shot back against the reports as incorrectly suggesting that Caine was “against us going to war with Iran”. (The reports only said that Caine had warned Trump of the consequences of a strike.)

“General Caine, like all of us, would like not to see War but, if a decision is made on going against Iran at a Military level, it is his opinion that it will be something easily won,” Trump wrote on Truth Social. Caine “has not spoken of not doing Iran, or even the fake limited strikes that I have been reading about, he only knows one thing, how to WIN and, if he is told to do so, he will be leading the pack”.

The Guardian has previously reported that Trump has not decided whether to launch strikes against Iran and that his decision will hinge on the results of talks in Geneva later this week with top Iranian officials. The US delegation will be led by Steve Witkoff, his longtime friend and Middle East envoy, as well as his son-in-law, Jared Kushner.

The other main advisers include the vice-president, JD Vance; the secretary of state, Marco Rubio; the CIA director, John Ratcliffe; the defense secretary, Pete Hegseth; the White House chief of staff, Susie Wiles; and the director of national intelligence, Tulsi Gabbard.

Trump could either order a limited military strike intended to influence negotiations between Iran and the US or could launch a much larger offensive meant to decapitate the government of Iran.

“We could go now,” said Charles Wald, a retired air force general and former deputy commander of US European Command, who said that the arrival of the USS Gerald Ford near Crete would give additional capability to protect Israel from a potential Iranian counterattack.

The military buildup and Trump’s ultimatums to Iran ultimately could force him into action, Wald added.

“The problem is that Trump has … kind of implied a red line,” said Wald, who now serves as a distinguished fellow at the Jewish Institute for National Security of America. “If they don’t get the agreement, and then they don’t do anything, it’s going to be twice as bad as when Obama didn’t do anything in Syria for the chemical weapons.”