Iran and the United States held a fifth round of negotiations over Tehran's rapidly advancing nuclear program in Rome on Friday, with enrichment emerging as the key issue. U.S. officials up to President Donald Trump insist Iran cannot continue to enrich uranium at all in any deal that could see sanctions lifted on Tehran's struggling

The United States wants to prevent a nuclear arms race. Iran insists its production is peaceful, but it has lied about operations before.

Iran's foreign minister described nuclear talks with the United States as "complicated", following the conclusion of a fifth round of discussions in Rome on Friday.The talks, which began in April, are the highest-level contact between the foes since the United States quit a landmark 2015 nuclear accord during President Donald Trump's first term.