US Ambassador to Britain Woody Johnson said Iran needed to make tangible and sustained changes to behave like a normal country.
“Until then, America is turning up the pressure and we want the UK by our side,” Johnson wrote in the Sunday Telegraph newspaper.
“It is time to move on from the flawed 2015 deal. We are asking global Britain to use its considerable diplomatic power and influence and join us as we lead a concerted global effort toward a genuinely comprehensive agreement.”
Asked about Johnson’s article, the British foreign office pointed to comments from Middle East minister Alistair Burt, who last week ruled out Britain going along with the United States. Burt said the deal was an important part of regional security and that, with the European Union, the government was trying to protect British companies from the US sanctions when dealing with Iran.
The United States reimposed stiff economic sanctions on Iran on Monday, ratcheting up pressure on the Islamic Republic despite statements of deep dismay from European allies, three months after President Donald Trump pulled the US out of the 2015 nuclear deal between Tehran and world powers.
A first set of reimposed US sanctions affect financial transactions that involve US dollars, Iran's automotive sector, the purchase of commercial planes and metals including gold.
A second batch of US sanctions targeting Iran's oil sector and central bank are to be reimposed in early November.
Trump warned that those who don't wind down their economic ties to Iran "risk severe consequences."