The US plans to cut its troop presence in Syria by half, consolidating bases as part of a broader regional military review.
Khamenei said Tehran retains a "very pessimistic" overall view of the US and should not tie its national affairs to nuclear negotiations.
Iran's "hobbled economy" is likely to keep them at the negotiating table, the Wall Street Journal reported on Sunday.
Trump, who has threatened military action if no deal is reached on halting Iran's nuclear program, told reporters aboard Air Force One that he met with advisers on Iran and expected a quick decision.
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The US and Iran are set for talks in Oman, as President Trump threatens military action if Iran doesn't limit its nuclear program, while US troops remain stationed across the Middle East.
Trump warned Iran to abandon its nuclear program or face harsh consequences.
The US sanctioned five Iranian entities for nuclear activity, just days before planned nuclear talks in Oman, as Trump warns of consequences if talks fail.
Iranians are cautiously hopeful ahead of US nuclear talks, as markets rise and the rial strengthens, but fears of failure and conflict linger.
The bleak assessment from Moscow comes amid the disintegration of the tangle of arms control treaties which sought to slow the arms race and reduce the risk of nuclear war.