Washigngton, DC — (CNN) Discord between President Donald Trump and his chief diplomat is at an all-time high, spilling into public view in recent days, peaking with a NBC News report Wednesday that Secretary of State Rex Tillerson called Trump a “moron” in a Pentagon meeting.

Trump was aware before Wednesday’s report that Tillerson had referred to him as a “moron” at the Pentagon this summer, a source familiar with the conversation told CNN, but it’s unclear whether Trump discussed the remark with Tillerson. Trump was not present at the Pentagon meeting. A White House source also confirmed to CNN that Trump knew about the insult prior to Wednesday.

During a hastily arranged statement Wednesday morning, Tillerson insisted he enjoys a close relationship with Trump and called him “smart.” But he would not directly deny that he’d called Trump a “moron.”

“I’m not going to deal with petty stuff like that,” Tillerson said from the State Department Treaty Room. “I’m just not going to be part of this effort to divide this administration.”

Though Tillerson didn’t deny calling Trump a moron, Trump tweeted: “The @NBCNews story has just been totally refuted by Sec. Tillerson and @VP Pence. It is #FakeNews. They should issue an apology to AMERICA!”

Sources say Vice President Mike Pence has become a bit of a sounding board for Tillerson, and the two men often have lunch together. After the “moron” remark, an aide says Pence advised Tillerson on “setting expectations” and counseled him on how to work with the administration toward the President’s goals.

Pence’s spokesman denied Pence discussing with Tillerson the chief diplomat’s potential resignation.

“At no time did he and the secretary ever discuss the prospect of the secretary’s resignation from the administration. Any reporting to the contrary is categorically false,” said Jarrod Agen, Pence’s spokesman.

A senior White House adviser said there is “certainly some friction there to say the least” between Tillerson and the White House but pointed fingers at West Wing staff rather than directly at the President. This person said Tillerson is “obviously growing frustrated because of the unpredictable nature of his job.”

But Trump isn’t the only person in the West Wing who Tillerson has been at odds with. He became so “irate” with national security adviser H.R. McMaster earlier this year on a conference call that Defense Secretary James Mattis had to step in, an administration official directly familiar with the incident says.

“Tillerson and McMaster do not do well together,” said the official, who left the administration several weeks ago in an unrelated matter.

This person, who is directly familiar with other multiple interactions involving Tillerson, declined to be identified because of the sensitivity of the matter.

During that conference call, Tillerson, Mattis and McMaster were discussing the way ahead on the proposed strategy for fighting the war in Afghanistan. McMaster was pressing for a faster decision-making process from the Pentagon and State Department. As the official described it, Tillerson finally became so irritated with the White House pressure, he said they could move ahead without him. It is not clear if that was a threat to resign.

“Voices were raised” during that call, the official said. Mattis then stepped in and reminded McMaster that the State Department and Pentagon did not have a significant number of Senate-confirmed senior staff officials who could quickly work these problems. The official said McMaster then realized “he overstepped” and backed off.

But the official also describes a series of meetings and interactions in which Tillerson has become repeatedly irritated. The official said Mattis has tried to “mentor” Tillerson and treates him “with the respect of a peer, with talent, but maybe a guy without the political skills.”

The official described private meetings in which Tillerson has become “a little more hotheaded” than he appears in public, using salty language, a trait that Mattis shares.

Though Tillerson’s departure seems imminent, the friction between the President and his top diplomat may not have reached its boiling point yet. A person close to Tillerson said it has always been his plan to stay on at the State Department through the first year of the Trump administration but acknowledged again Wednesday that his future is “up to the President.”

Trump recently seemed to undercut Tillerson when he said he was wasting his time attempting new dialogue with North Korea.

“I told Rex Tillerson, our wonderful secretary of state, that he is wasting his time trying to negotiate with Little Rocket Man,” Trump wrote on Twitter. “Save your energy Rex. we’ll do what has to be done!”

Despite this, White House press secretary Sarah Sanders said Monday that Trump still had confidence in Tillerson, despite their different messages on North Korea.

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