The leaders of the United States, Germany, France and Britain on Saturday expressed their "grave and growing concern" at Iran's nuclear activities, after a meeting on the sidelines of the G20 summit.
"We are convinced that it remains possible to quickly reach and implement an understanding on return to full compliance," they said in a joint statement.
"This will only be possible if Iran changes course."
Earlier this week, Tehran said it would resume talks with world powers in November on reviving the 2015 Joint Comprehensive Plan of Action (JCPOA) on Iran's nuclear programme, following a five-month gap.
Iran held six rounds of indirect negotiations in Vienna with President Joe Biden's administration on returning to the agreement, but talks went on hiatus in June as a new hardline government took office in Tehran.
After the meeting in Rome, US President Joe Biden, French President Emmanuel Macron, German Chancellor Angela Merkel and British Prime Minister Boris Johnson "agreed that continued Iranian nuclear advances and obstacles to the IAEA's work will jeopardise the possibility of a return to the JCPOA".
The International Atomic Energy Agency (IAEA) is supposed to monitor Iran's nuclear activities.
In a joint statement, the leaders said they were determined "to ensure that Iran can never develop or acquire a nuclear weapon".
They said they shared a "grave and growing concern that, while Iran halted negotiations on a return to the JCPOA since June, it has accelerated the pace of provocative nuclear steps, such as the production of highly enriched uranium and enriched uranium metal".
"Iran has no credible civilian need for either measure, but both are important to nuclear weapons programs," the statement said.
The accord between Iran and six world powers to find a long-term solution to the crisis over its controversial nuclear programme has been moribund since former US president Donald Trump walked out in May 2018 and imposed sweeping sanctions.
Biden, his successor, has said he is ready to re-enter the agreement so long as Iran also returns to full compliance by rolling back nuclear activities that it undertook in response to Trump's sanctions.
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