Iran's Revolutionary Guard orders companies to defy US sanctions and trade with Tehran

US President Trump's crackdown on Iran faces its biggest test as a US rival dares Washington to act, ordering companies to ignore US sanctions against Iran. The move is seen as a challenge to US authority and could escalate tensions in the region. This comes as tensions between the US and Iran remain high following the downing of a US drone last month. The situation is closely watched by global markets and diplomatic observers.