US President Donald Trump has warned Iran's authorities against killing peaceful protesters, saying Washington will come to their rescue.
In a brief post on social media, he wrote: We are locked and loaded and ready to go. He gave no further details.
A senior adviser to Iran's Supreme Leader, Ayatollah Ali Khamenei, responded by saying Trump should be careful if he intervened, warning of potential chaos across the Middle East.
At least six people are reported to have been killed in Iran on Thursday after almost a week of mass protests sparked by worsening economic conditions.
In Trump's statement on Truth Social, he elaborated: If Iran shots [sic] and violently kills peaceful protesters, which is their custom, the United States of America will come to their rescue.
Khamenei adviser Ali Larijani warned shortly afterwards that any US interference would destabilise the entire region and also harm American interests.
Trump did not specify what action Washington could take against the Iranian authorities.
Earlier this year, the US carried out strikes against Iran's nuclear sites on Trump's orders, which officials claimed had set back Tehran's nuclear ambitions, a claim disputed by Iran.
In retaliation, Iran launched a missile attack on a major US military base in Qatar.
On the ground in Iran, protests that began due to economic grievances are intensifying, with reports of violence leading to fatalities among demonstrators and security personnel alike.
The protests, now spreading to various cities including Tehran, have been characterized by calls for significant political change, including ending Khamenei's rule.
President Masoud Pezeshkian stated he would listen to the legitimate demands of protesters, while warning of a decisive response to attempts at destabilization.
