US Vice President JD Vance told Iran on Wednesday to take Washington's threats of military action "seriously," a day after President Donald Trump appeared to build the case for war in his State of the Union address.
As US forces mass in the Middle East, Trump claimed in his speech to Congress on Tuesday that Iran was seeking to develop missiles that can strike the United States.
Trump also accused Iran, whose negotiators will meet US officials in Geneva on Thursday, of having "sinister nuclear ambitions" and working to rebuild a nuclear programme that was targeted by US strikes last year.
Vance told Fox News that while Trump was going to try to "accomplish it diplomatically," the US president also had the "right" to use military action.
"You can't let the craziest and worst regime in the world have nuclear weapons," said Vance.
"The president has several other tools at his disposal to ensure this doesn't happen. He's shown a willingness to use them, and I hope the Iranians take it seriously in the negotiations tomorrow because that's certainly what the president prefers."
His comments came as the United States announced fresh sanctions targeting Iran, pressing on with what Washington calls its "maximum pressure" campaign.
US Secretary of State Marco Rubio later said Iran’s refusal to discuss its ballistic missile programme was "a big problem".
"It's also important to remember that Iran refuses, refuses to talk about the ballistic missiles to us or to anyone, and that's a big problem," Rubio told reporters in St. Kitts, where he attended a meeting of Caribbean Community leaders.
Rubio said Iran "poses a very great threat to the United States" and accused Tehran of trying to rebuild elements of its nuclear programme.
"They're not enriching right now, but they're trying to get to the point where they ultimately can," he said.
He added that Iran possesses a large number of ballistic missiles, particularly short-range missiles that threaten US bases and partners in the region, including in the UAE, Qatar and Bahrain.
He also cited naval capabilities that could endanger shipping and US forces.
Iran's President Masoud Pezeshkian said there was a "favourable outlook" for negotiations, while Foreign Minister Abbas Araghchi travelled to Switzerland for talks.
Tehran rejected Trump’s missile claims as "big lies" and maintains its nuclear programme is for civilian purposes.
