Washington is pressing on with its stated mission of making Iran "radioactive" to the world, this week designating its elite Islamic Revolutionary Guards Corps (IRGC) as a foreign terrorist organisation, the tag it applies to Lebanese Hizbollah and Palestinian Hamas among others. It was the first time that the United States has thus labelled an agency of a foreign government. This has broad implications. Secretary of State Mike Pompeo justified the move as stemming from Iran's "use of terrorism as a tool of statecraft". The main objective is to maintain maximum pressure on Iran, force it back to the negotiating table and win its compliance with US goals such as Teheran surrendering the right to enrich uranium, ceasing support for militant groups and refraining from threatening Israel.

President Donald Trump's intent in pursuing the course is not in much doubt. Since taking office, his administration has already sanctioned more than 970 Iranians and organisations and withdrawn from the landmark 2015 nuclear deal. The effectiveness of this punitive approach, however, remains to be proven. Taking IRGC in ambit means targeting an entity that commands more than 100,000 troops, has a hand in the nation's ballistic missiles and nuclear programme and operates the secretive Al Quds force that aids militias in Syria, Yemen, Iraq and Lebanon. The strategy - a sharp contrast to Mr Trump's engagement policy with another "rogue" nation, North Korea - makes clear that the door to diplomacy has been shut. It strengthens the cause of hardliners in Iran and can cause an escalation in hostilities. Iran's tit-for-tat response was to designate the US Central Command, which runs military operations in the Middle East and Afghanistan, as a terrorist group. The US then moved to put its troops on alert for retaliatory attacks.