The E3 letter follows months of diplomatic stalemate, particularly after a 12-day war between Iran and Israel in June.

The top diplomats of Britain, France, and Germany threatened to reimpose sanctions on Iran as an end-of-the-month deadline nears for the country to resume negotiations with the West over its nuclear program and cooperation with the United Nations nuclear watchdog.

The UK, France and Germany have told the UN they are ready to reimpose sanctions on Iran over its nuclear programme if it fails to resume talks by the end of August. The three countries, known as the E3, said they were prepared to trigger a "snapback" mechanism - meaning previous sanctions would be reinstated - unless Iran resumes negotiations.