White House Press Secretary Sarah Sanders said that the tweet from President Trump to Iranian President Hassan Rouhani confirms his intolerance to nuclear proliferation.

Trump warned Rouhani directly in the all-caps message to "never, ever threaten the United States again" and that America will not stand for his "demented words of violence." 

Rouhani had previously given Trump a warning of his own, saying that going to war with his country would be "the mother of all wars."

"Mr. Trump, don't play with the lion's tail. This would only lead to regret. America should know that peace with Iran is the mother of all peace, and a war with Iran is the mother of all wars."

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Sanders said Monday that Trump has been clear since day one of his presidency that he'd aggressively stand up to the "empty threats" of other international leaders.

"You can be rest-assured, he takes this process extremely seriously," Sanders said of Trump, adding that he's monitoring Iran's actions.

In May, President Trump announced his decision to withdraw the United States from the Iran nuclear deal, citing what he called the country's "bloody ambitions."

Israeli Prime Minister Benjamin Netanyahu had previously unveiled intelligence that found Iran was "brazenly lying" about its nuclear weapons development.

"[President Trump is] also not afraid to take tough steps if necessary," Sanders said.

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