President Donald Trump said on Friday that the United States was "locked and loaded" to respond if Iran killed protesters, prompting Tehran to warn that intervention would destabilise the region.

Protesters and security forces clashed in several Iranian cities on Thursday, with six people reported killed, the first deaths since the unrest escalated.

Shopkeepers in the capital Tehran went on strike on Sunday over high prices and economic stagnation, actions that have since spread into a protest movement that has swept into other parts of the country.

Trump said on his Truth Social platform that if Iran "violently kills peaceful protesters, which is their custom, the United States of America will come to their rescue".

"We are locked and loaded and ready to go," he added.

Iranian Foreign Minister Abbas Araghchi called Trump's remarks "reckless and dangerous", and warned that the armed forces were "on standby" in the event of any intervention.

The head of Iran's top security body, Ali Larijani, warned Trump that "US interference in this internal matter would mean........

© Al Monitor