The US Treasury Department has instructed banks to monitor and flag suspected Iranian money-laundering networks used to smuggle sanctioned oil, amidst shaky ceasefire talks with Iran.

The Treasury Department wants US banks and other financial institutions to monitor for suspected Iranian money-laundering networks that use their funds to smuggle sanctioned oil through shell companies and cryptocurrency networks. The move, which effectively deputises the global financial system to help disrupt Iran’s sanctions-evasion infrastructure, comes as the US and Iran reached another impasse over how to end their war while their ceasefire has grown increasingly shaky. US President Donald...