Borrell said of Iran's latest response to an EU-drafted text last week, which hardened Tehran's demands on Washington, "if the purpose is to close the deal quickly, it is not going to help it".

On August 7, Borrell put forward what he called a final text to restore the 2015 accord, which was abandoned by former US president Donald Trump in 2018.

Talks to revive the nuclear deal known as the Joint Comprehensive Plan of Action have been ongoing in Vienna since April 2021, and in recent weeks Iran and Washington have been responding to the EU text.

On Thursday, however, Washington said that Iran's latest proposed changes to the text were "not constructive" and on Monday Iran complained that it had not yet received an official US response.

Speaking at a news conference in Brussels, Borrell said that his initial "carefully balanced" text had been "well received" and that initially it had seemed the parties were converging on a common position.

"But the last interaction is not converging, it is diverging," he said. "That is very much worrisome, if the process does not converge. The whole process is in danger.

"So I have to say that the last answer I got, if the purpose is to close the deal quickly, it is not going to help it," he said.

"So what I'm doing to keep consulting with all other JCPOA participants, and in particular the US.

"But I'm sorry to say that I am less confident today than 28 hours before about the convergence of the negotiation process and about the prospect of closing the deal right now."