The US has threatened to impose severe sanctions against any country or entity maintaining economic ties with Iran, hoping to achieve with economic measures what military means have so far failed to do.It is unclear, however, how far the Trump administration is prepared to go in confronting China, Iran’s biggest trading partner, which has signalled its resistance to US economic pressure to cut off links with an ally.Iran, meanwhile, vowed retaliation against any country that took part in the US-led isolation campaign.Launching what he called Operation Economic Outcast, the US treasury secretary, Scott Bessent, called it an unprecedented campaign and…