The decision Wednesday was the latest blow by President Donald Trump to the 2015 international deal to curb Iran's nuclear programme, which Brussels has been trying to salvage.

"We regret this decision," said Carlos Martin Ruiz De Gordejuela, a spokesman for EU diplomatic chief Federica Mogherini.

"From our side, we will continue to work with Mr Zarif as Iran's most senior diplomat and in view of the importance of maintaining diplomatic channels," Martin said.

The US government announced Wednesday it was freezing any of Zarif's assets in the United States or that are controlled by US entities, adding it also will curtail his international travel.

Trump last year pulled out of a 2015 deal struck by his predecessor Barack Obama, EU powers, China and Russia aimed at curbing Iran's nuclear programme.

The EU has been trying to salvage the deal ever since.

Zarif has been at the heart of complex talks with foreign capitals over Iran's nuclear power industry, which Tehran says is peaceful, but Washington and regional allies including Israel insist is cover for a secret weapons programme.

But a senior Trump administration official said that Zarif's diplomatic image -- bolstered by his fluent English, self-effacing humor and background as a US-educated academic -- was false.