Washington has called on international financial institutions to steer clear of doing business with Iran’s central bank, in the US’s most wide-ranging attempt yet to isolate Tehran financially.

The Treasury department has issued a warning of the risks of doing business with 51 state-owned and seven privately held Iranian banks – in effect the whole of Iran’s banking sector. The list includes institutions specialising in export financing and foreign investment, as well as Iranian state-owned banks located as far away as Venezuela, Hong Kong and the UK.