The accusations against Standard Chartered, which has been described by a New York banking regulator as a “rogue institution” because of its dealings with Iran, have underlined the new-found determination of US authorities to enforce the wide-ranging sanctions on Iran, writes Geoff Dyer in Washington.

Within the space of a few weeks, US authorities have denounced two of the largest British banks, imposed sanctions on a Chinese bank owned by the country’s largest company and introduced a new round of sanctions on companies doing business with Iran.

While Iran has been subject to sanctions for years, the new US focus on enforcement and toughening the rules is the result of fears over an imminent Israeli military strike on Iran and the politics of a presidential election in which Iran is one of the few prominent foreign policy issues.