Secretary of State Rex Tillerson's frustration with President Trump rose to such a level that he called his boss "a moron" after a July 20 Pentagon meeting and considered resigning over the summer, NBC News reported Wednesday morning.

Citing unnamed senior administration officials, NBC News said the "moron" comment came after Tillerson met with members of Trump's national security team and Cabinet officials.

The report said that while it's unclear whether Vice President Pence was aware of the incident, sources say he counseled Tillerson, giving him tips to ease tensions with the president.

Tensions between Trump and Tillerson seemed apparent on Sunday, with Trump on tweeting that Tillerson is "wasting his time" by negotiating with North Korean leader Kim Jong Un.

“I told Rex Tillerson, our wonderful Secretary of State, that he is wasting his time trying to negotiate with Little Rocket Man,” the president tweeted, using his nickname for North Korea's leader. “Save your energy Rex, we'll do what has to be done!”

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