"The next round of Iran-US indirect talks is being planned for next Sunday in Muscat," foreign ministry spokesman Esmaeil Baqaei said in a statement Tuesday, adding foreign minister and chief negotiator Abbas Araghchi would this week attend the Norway's Oslo Forum, a gathering of conflict mediators.

Iran and the United States have held five rounds of talks since April to thrash out a new nuclear deal to replace the 2015 accord with major powers that Trump abandoned during his first term in 2018.

On May 31, after the fifth round of talks, Iran said it had received "elements" of a US proposal for a nuclear deal, with Araghchi later saying the text contained "ambiguities".

Iran said on Monday the US proposal was "lacking elements" reflective of the previous negotiations and that it would present a "reasonable, logical and balanced" counter-proposal to the United States through mediator Oman.

Trump has said new US-Iran talks this week could clarify if a nuclear deal is possible to avoid military action.

He added that the latest meeting with Iran was expected Thursday, although a source familiar with preparations said it would more likely be on Friday or Saturday.

Iran and the United States have recently been locked in a diplomatic standoff over Iran's uranium enrichment, with Tehran defending it as a "non-negotiable" right and Washington calling it as a "red line".

Iran currently enriches uranium to 60 percent, far above the 3.67-percent limit set in the 2015 deal and close though still short of the 90 percent needed for a nuclear warhead.

Western countries, including the United States, have long accused Iran of seeking to acquire atomic weapons, while Tehran insists its nuclear programme is for peaceful purposes.