By Sam Wilkin

DUBAI (Reuters) - Iran's Supreme Leader Ayatollah Ali Khamenei told military commanders on Sunday the United States had created the "myth" of nuclear weapons to portray Iran as a threat, hardening his rhetoric before nuclear negotiations resume this week.

Khamenei, the highest authority in Iran, has supported the nuclear talks but continues to express deep mistrust of the United States.

"They created the myth of nuclear weapons so they could say the Islamic Republic is a source of threat. No, the source of threat is America itself, with its unrestrained, destabilizing interventions," Khamenei said in a televised address to a hall of several hundred military commanders.

"The other side is methodically and shamelessly threatening us militarily ... even if they did not make these overt threats, we would have to be prepared," he said.

Political leaders in Iran and the United States have to contend with domestic constituencies skeptical about the outcome of the talks. Khamenei's comments did not appear to suggest he has withdrawn his cautious support for the diplomatic process.

Iran and six world powers including the United States reached a framework accord on Iran's disputed nuclear program this month and will resume negotiations in Vienna this week, aiming to reach a final deal by the end of June.

The framework accord is a step towards a settlement that would allay Western fears that Iran could build an atomic bomb, with economic sanctions on Tehran being lifted in return.

Despite significant progress, the two sides still disagree on several issues, including how quickly international sanctions would be lifted under a final deal.

"NATIONAL HUMILIATION"

Earlier this month, Khamenei insisted that all sanctions be lifted immediately on a deal being reached, a condition the U.S. State Department dismissed. He warned of Washington's "devilish" intentions, even as he reaffirmed his support for Iran's negotiating team.

The deputy commander of the powerful Islamic Revolutionary Guards Corps (IRGC) on Sunday rejected any inspections of military sites as a "national humiliation", highlighting another area of difference between the two sides.

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"This subject is treasonous and selling out the country, and if anyone speaks of it we will respond with hot lead," Hossein Salami said, in comments cited by state news agency IRNA.

Republican U.S. Senator Bob Corker, the co-author of legislation that would allow Congress to review any final nuclear deal with Iran, told CNN on Sunday that lifting of sanctions must be phased to ensure Iran's compliance and include broad inspection capabilities for military sites.

Senator Marco Rubio, a Republican 2016 presidential candidate, said the agreement thus far leaves too much infrastructure in place for Iran to develop a nuclear weapon.

He told the CBS program "Face the Nation" that U.S. and international sanctions must remain in place, with a warning of U.S. military action if certain thresholds are crossed.

"We don't want that to happen, but risk of a nuclear Iran is so great that option must be on the table," Rubio said.

Khamenei also criticized U.S. support for a Saudi-led offensive in Yemen, where a coalition of Arab countries is bombing Iran-allied Houthi rebels who seized the capital Sanaa last year and took control of other parts of the country.

"Today these tragic events are happening in Yemen and the Americans are supporting the oppressor," he said.

The four-week old campaign, in which Iran and Western countries have backed opposite sides, began during the last round of nuclear talks. Growing civilian casualties and Western suspicions that Iran is arming the Houthis have added to tensions.

(Additional reporting by David Lawder in Washington; Editing by Gareth Jones)