The United States and Iran will hold a new round of nuclear talks Sunday in Oman ahead of a visit to the region by Donald Trump, whose key negotiator staked out an increasingly hard line on the issue of uranium enrichment. Trump, who will visit three other Gulf Arab monarchies next week, has voiced hope for reaching a deal with Tehran to avert an Israeli military strike on Iran’s nuclear program that could ignite a wider war. Three previous rounds of talks in Oman and Rome ended with notes of optimism, with the two sides saying the atmosphere was friendly despite the countries’ four decades of enmity. But they are not believed to have gone into technical detail, and basic questions remain. Steve Witkoff, Trump’s friend who has served as his globe-trotting negotiator on issues including on Iran, had initially suggested flexibility on Tehran maintaining low-level enrichment of uranium for civilian purposes. But in an interview published Friday, Witkoff gave his clearest message yet that the Trump administration would oppose any enrichment. “An enrichment program can never exist in the state of Iran ever again. That’s our red line. No enrichment,” he told right-wing Breitbart News. “That means dismantlement, it means no weaponization, and it means that Natanz, Fordow and Isfahan — those are their three enrichment facilities — have to be dismantled,” he said. US Secretary of State Marco Rubio earlier raised the possibility of Iran importing enriched uranium for any civilian energy. Trump in his first term withdrew from a nuclear agreement with Tehran negotiated by former president Barack Obama that allowed Iran to enrich uranium at levels well below what is needed for weapons.