It came as European powers and the United States submitted a censure motion to the UN’s nuclear watchdog in an effort to ramp up pressure on Iran, in spite of Tehran’s warnings.
Iran has said it will present a counter-proposal to the latest draft from Washington, which it had criticised for failing to offer sanctions relief in return for curbs on its nuclear programme.
“The next round of Iran-US indirect talks is being planned for next Sunday in Muscat,” Iranian foreign ministry spokesman Esmaeil Baqaei said in a statement on Tuesday.
There was no immediate comment from mediator Oman, which has hosted some of the previous rounds, while Washington has said the talks could be held as early as Thursday.
The longtime foes have held five rounds of negotiations since April, the highest level contact since President Donald Trump withdrew Washington from a 2015 nuclear accord during his first term.
Trump has said the next meeting was expected on Thursday, although a source familiar with preparations said it would more likely be on Friday or Saturday.
Iran’s top negotiator, Foreign Minister Abbas Araghchi, will be attending the annual Oslo Forum in Norway on Thursday, his office said.
On May 31, after the fifth round of talks, Iran said it had received “elements” of a US proposal for an agreement, which Araghchi has criticised for its “ambiguities”.
Tehran has said the offer failed to include issues raised in previous negotiations including the lifting of sanctions — a key demand for Tehran, which has been reeling under their weight for years.
On Monday, foreign ministry spokesman Baqaei said Iran would present a “reasonable, logical and balanced” counter-proposal.