Delegates from the United States and Iran are holding talks in Oman on Saturday in a delicate effort to restart negotiations over Tehran’s controversial nuclear program. 

The talks, between a mediator to Iran's Foreign Minister Abbas Araghchi and U.S. Mideast envoy Steve Witkoff, come nearly seven years after President Donald Trump unilaterally withdrew the U.S. from Tehran's nuclear deal with world powers in 2018. Since then, indirect talks between the two adversaries have made zero progress.

Trump has imposed new sanctions on the Islamic Republic as part of his "maximum pressure" campaign and has suggested military action remained a possibility. Despite this, the president has said he still believed a new deal could be reached by writing a letter to Iran's 85-year-old Supreme Leader Ayatollah Ali Khamenei, which he sent early last month. 

Khamenei, meanwhile, has warned that Iran would respond to any U.S.-led attack with an attack of its own.

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"They threaten to commit acts of mischief, but we are not entirely certain that such actions will take place," the supreme leader said. "We do not consider it highly likely that trouble will come from the outside. However, if it does, they will undoubtedly face a strong retaliatory strike."

Iranian Foreign Ministry spokesperson Esmail Baghaei called such threats against Iran "a shocking affront to the very essence of International Peace and Security."

"Violence breeds violence, peace begets peace. The US can choose the course...; and concede to CONSEQUENCES," he wrote on X.

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Iranian President Masoud Pezeshkian has rejected direct negotiations with the United States over Tehran's nuclear program.

"We don't avoid talks; it's the breach of promises that has caused issues for us so far," Pezeshkian said in televised remarks during a Cabinet meeting. "They must prove that they can build trust."

Once allies, both countries have been hostile to one another for nearly half a century, following the 1979 Islamic Revolution that saw the creation of a theocratic government led by Grand Ayatollah Ruhollah Khomeini.

Shah Mohammad Reza Pahlavi, whose rule was cemented in a CIA-led coup in 1953, had fled Iran before the revolution, ill with cancer, as demonstrations swelled against his rule. Late in 1979, university students overran the U.S. Embassy in Tehran, seeking the shah's extradition and sparking the 444-day hostage crisis that severed diplomatic relations between Iran and the U.S.

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In the decades since, Iran-U.S. relations have see-sawed between enmity and grudging diplomacy, with relations peaking when Tehran made the 2015 nuclear deal with world powers before Trump withdrew from the deal, sparking more tensions in the Mideast that persist today.

Under the original 2015 nuclear deal, Iran was allowed to enrich uranium up to 3.67% purity and to maintain a uranium stockpile of 661 pounds. The last report by the International Atomic Energy Agency on Iran's program put its stockpile at 18,286 pounds as it enriches a fraction of it to 60% purity.

U.S. intelligence agencies assess that Iran has yet to begin a weapons program, but has "undertaken activities that better position it to produce a nuclear device, if it chooses to do so."

Iran has insisted for decades that its nuclear program is peaceful. However, its officials increasingly threaten to pursue a nuclear weapon. Iran now enriches uranium to near weapons-grade levels of 60%, the only country in the world without a nuclear weapons program to do so.