The United States has imposed sanctions on Iranian Foreign Minister Mohammad Javad Zarif, the latest move by Washington in its maximum pressure campaign against Tehran.

The Treasury Department said on Wednesday that it was imposing sanctions on Zarif, for acting on behalf of Iranian Supreme Leader Ayatollah Ali Khamenei.

In a statement Treasury Secretary Steven Mnuchin said Javad Zarif implements the reckless agenda of Iran's Supreme Leader, and is the regime's primary spokesperson around the world.

Zarif brushed off the sanctions on Twitter, saying the US move indicated Washington saw him as a "threat".