Tehran has approached the talks warily, doubting the likelihood of an agreement and suspicious of Trump, who has threatened to bomb Iran if there is no deal.
Trump warned Iran to abandon its nuclear program or face harsh consequences.
With Iran's alliances weakening and US military threats rising, Oman provides a discreet, neutral venue for a possible last bid to resolve the nuclear standoff.
Moscow may think that it can link a Ukraine deal to a deal that will also help Iran.
Over the weekend, US President Donald Trump posted a backhanded threat to the Houthis and Iran on his platform Truth Social.
Khamenei, Iran’s cowardly, war-mongering, and delusional dictator, continues to portray himself as God’s representative on Earth.
Tougher Iran oil sanctions under Trump could cut exports; China’s cooperation remains a complex factor.
In his first public appearance since Tuesday's missile attack , Ayatollah Ali Khamenei said that Iran's axis of resistance remains undeterred.
For years, US intelligence agencies have maintained that Iran was not engaged in the key activities necessary to develop a testable nuclear device.
At least five US personnel were injured in an attack against a military base in Iraq on Monday, US officials told Reuters.