Iran vowed to shut down all oil exports from the Gulf as the United States prepared to roll out economic sanctions on Monday, threatening Tehran with what it called 'the greatest financial offensive ever marshalled'.

Iran warns of a devastating response as the US prepares tougher sanctions, while falling oil flows through Hormuz raise concerns over global energy supplies.

Tehran says Washington's plan to turn up economic pressure contradicts international law; oil traffic through Hormuz still near a standstill