Dubai, May 11 (AP) Iran and the United States began a fourth round of negotiations Sunday over Tehran's rapidly advancing nuclear programme, officials said, just ahead of a visit by President Donald Trump to the Middle East this week.

The round of talks, again happening in the sultanate of Oman, likely will see Oman's Foreign Minister Badr al-Busaidi mediating. American officials believe the talks will include both indirect and direct portions, as in previous rounds of negotiations, but like the other rounds in Muscat and Rome, details remain scarce.

The talks seek to limit Iran's nuclear programme in exchange for the lifting of some of the crushing economic sanctions the US has imposed on the Islamic Republic, closing in on half a century of enmity.

Trump has repeatedly threatened to unleash airstrikes targeting Iran's programme if a deal isn't reached. Iranian officials increasingly warn that they could pursue a nuclear weapon with their stockpile of uranium enriched to near weapons-grade levels. Meanwhile, Israel has threatened to strike Iran's nuclear facilities on their own if it feels threatened, further complicating tensions in the Mideast already spiked by the Israel-Hamas war in the Gaza Strip.

Iranian state television announced the talks had begun. There was no immediate comment from the US side.

The fourth round comes ahead of Trump's trip The talks will again see Iranian Foreign Minister Abbas Araghchi and US Mideast envoy Steve Witkoff lead the negotiations. They have met and spoken face-to-face in the talks, but the majority of the negotiations appear to have been indirect, with al-Busaidi shuttling messages between the two sides.

Iran has insisted that keeping its ability to enrich uranium is a red line for its theocracy. Witkoff also has muddied the issue by first suggesting in a television interview that Iran could enrich uranium at 3.67%, then later saying that all enrichment must stop.

“An enrichment program can never exist in the state of Iran ever again,” Witkoff told the right-wing Breitbart news site in a piece published Friday. “That's our red line. No enrichment. That means dismantlement, it means no weaponisation, and it means that Natanz, Fordow, and Isfahan — those are their three enrichment facilities — have to be dismantled.” Araghchi, however, warned again that enrichment remains a red line for Iran.

“This is a right of the Iranian people that is not up for negotiation or compromise. Enrichment is one of the achievements and honors of the Iranian nation,” Araghchi said before leaving Tehran. “A heavy price has been paid for this enrichment. The blood of our nuclear scientists has been shed for it. This is absolutely non-negotiable. That has been our clear stance that we have always voiced.” Iran's 2015 nuclear deal with world powers capped Tehran's enrichment at 3.67% and reduced its uranium stockpile to 300 kg. That level is enough for nuclear power plants, but far below weapons-grade levels of 90%.

Since the nuclear deal's collapse in 2018 with Trump's unilateral withdrawal of the US from the accord, Iran has abandoned all limits on its programme and enriched uranium to up to 60% purity — a short, technical step from weapons-grade levels. There have also been a series of attacks at sea and on land in recent years, stemming from the tensions even before the Israel-Hamas war began.

Iran faces pressures at home as talks continue Iran also faces challenges at home, exacerbated by sanctions. Its troubled rial currency, once over 1 million to $1, has strengthened dramatically due to the talks alone to around 830,000 to $1.

However, the two sides still appear a long way from any deal, even as time ticks away. Iranian media broadly reported a two-month deadline imposed by Trump in his initial letter sent to Iran's Supreme Leader, Ayatollah Ali Khamenei. Trump said he wrote the letter on March 5, which made it to Iran via an Emirati diplomat on March 12 — putting the deadline in theory as Monday when Trump takes off from Washington for his trip to Saudi Arabia, Qatar and the United Arab Emirates.

Iran's internal politics are still inflamed over the mandatory hijab, or headscarf, with women still ignoring the law on the streets of Tehran. Rumours also persist over the government potentially increasing the cost of subsidised gasoline in the country, which has sparked nationwide protests in the past.

Meanwhile, the last round of talks in Oman on April 26 took place as an explosion rocked a southern Iranian port, killing dozens of people and injuring over 1,000 others. Iran still hasn't explained what caused the blast at the Shahid Rajaei port, which has been linked to a shipment of missile fuel components to the Islamic Republic. (AP) SCY SCY