US Secretary of State Rex Tillerson has accused Iran of "alarming ongoing provocations" to destabilise countries in the Middle East.
He levelled the charge as the Trump administration launches a review of its policy towards Iran.
Mr Tillerson said the review would not only look at Iran's compliance with a 2015 nuclear deal but also its behaviour in the region, which he said undermined US interests in Syria, Iraq, Yemen and Lebanon.
His tough words matched those of US Defense Secretary James Mattis, who said in a visit to Saudi Arabia yesterday that Iran's destabilising influence would have to be overcome to end the conflict in Yemen.
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Though there was no sign the Trump administration intended to walk away from the deal, Mr Tillerson twice cautioned that if left unchecked, Iran could become a threat like North Korea, which is also under pressure over its nuclear ambitions.
He said the 2015 nuclear deal between Iran and six world powers failed "to achieve the objective of a non-nuclear Iran and only delays their goal of becoming a nuclear state".
The next test of President Donald Trump's attitude towards the nuclear deal will come next month when he must decide whether to extend sanctions waivers for Iran first signed by former president Barack Obama.
During his presidential campaign, Mr Trump called the agreement "the worst deal ever negotiated".
The nuclear agreement, negotiated during Mr Obama's presidency, placed limitations on Iran's nuclear program in exchange for lifting economic sanctions against Iran.
