The longtime adversaries are set to meet on Saturday in Oman, weeks after a letter to Supreme Leader Ayatollah Ali Khamenei by US President Donald Trump, who sought diplomacy but warned of possible military action if Iran refuses.

"Far from putting up a show and merely talking in front of the cameras, Tehran is seeking a real and fair agreement, important and implementable proposals are ready," Khamenei adviser Ali Shamkhani posted on X.

He confirmed that Foreign Minister Abbas Araghchi was heading to Oman "with full authority for indirect negotiations with America", adding that if Washington showed goodwill, the path forward would be "smooth".

Ahead of the talks, Trump reiterated his opposition to Iran gaining a nuclear weapon.

"I want Iran to be a wonderful, great, happy country. But they can't have a nuclear weapon," Trump told reporters aboard Air Force One, hours before his envoy Steve Witkoff was due to meet Araghchi.

Witkoff, Trump's friend who serves as his globe-trotting envoy, sounded a note of flexibility ahead of the talks.

Witkoff told The Wall Street Journal that "our position today" starts with demanding that Iran completely dismantle its nuclear programme -- a view of hardliners around Trump that few expect Iran would ever accept.

"That doesn't mean, by the way, that at the margin we're not going to find other ways to find compromise between the two countries," Witkoff told the newspaper.

"Where our red line will be, there can't be weaponisation of your nuclear capability," Witkoff added.

Former US president Barack Obama negotiated a deal in 2015 that sought to prevent Iran from obtaining a nuclear weapon without insisting on full dismantlement of its contested programme.

Trump denounced the agreement as too weak and ripped it up after taking office the first time, instead imposing sweeping sanctions on Iran's oil sector.

Tehran adhered to the deal for a year before rolling back its own commitments.

- 'Hostile rhetoric' -

Ahead of the talks, Trump reiterated that military action was "absolutely" possible if they failed.

Iran responded by saying Tehran could expel United Nations nuclear inspectors, prompting in turn a US warning that this would be an "escalation".

Iran has consistently denied seeking to acquire nuclear weapons.

On Friday, foreign ministry spokesman Esmaeil Baqaei said Iran was "giving diplomacy a genuine chance in good faith and full vigilance".

"America should appreciate this decision, which was made despite their hostile rhetoric," he said.

On Thursday, Washington imposed additional sanctions on Iran, targeting its oil network and nuclear programme.

Iran's nuclear agency chief Mohammad Eslami downplayed their impact.

"They applied maximum pressure with various sanctions, but they were unable to prevent the country from progressing," he said.

"They still think that they can stop this nation and country with threats and intimidation, psychological operations, or stupid actions."

Ahead of the Oman talks, Witkoff -- who has also been seeking to end the Ukraine war -- visited Russia, which has close cooperation with Iran.

The European Union, which backed the Obama-era accord, said Friday that there was "no alternative to diplomacy" on the Iranian nuclear issue.

- Changed regional climate -

Trump announced the talks Monday during a visit to Washington by Israeli Prime Minister Benjamin Netanyahu, who has warned that military action will be "inevitable" if diplomacy drags on.

Iran and Israel have attacked each other directly for the first time since the October 2023 attack on Israel by Hamas, which enjoys support by Tehran.

Hamas in Gaza has suffered heavy losses, as has Iranian-backed Hezbollah in Lebanon. Iran's main ally among Arab leaders, Syria's Bashar al-Assad, was toppled in December.

While the West wants to include Iran's ballistic missile programme and regional influence in negotiations, Tehran maintains it will talk only about its nuclear programme.

"If the American side does not raise irrelevant issues and demands and puts aside threats and intimidation, there is a good possibility of reaching an agreement," deputy foreign minister Majid Takht-Ravanchi said.

Hardline Iranian media are sceptical about the talks.

The Kayhan newspaper warned that entering negotiations with the United States in a bid to lift sanctions was a "failed strategy".

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