Iran's nuclear negotiator said after talks with European Union mediators in Brussels that Tehran had agreed to resume talks in Vienna next month. These discussions had been on hiatus since June.

"We are prepared to return to Vienna, and we believe that it remains possible to quickly reach and implement an understanding on return to mutual full compliance" with the 2015 nuclear deal, a State Department spokesperson said.

The talks should focus on "closing the small number of issues that remained outstanding at the end of the sixth round of talks in June," he said.

"As we have also been clear, this window will not remain open forever as Iran continues to take provocative nuclear steps, so we hope that they come to Vienna to negotiate quickly and in good faith."

President Joe Biden has repeatedly offered to return to the nuclear accord reached in 2015 but his administration has voiced growing frustration at the prolonged delay, which comes as a new hardline government gets settled in Tehran.

Then president Donald Trump withdrew the United States from the deal in 2018 and imposed sweeping sanctions, leading Iran to step up contested nuclear work in protest.