A leader of an organization representing Native American tribes said Monday that President Trump calling Sen. Elizabeth WarrenElizabeth Ann WarrenSanders on difference with Warren: she's a capitalist 'I'm not' Rubio hits Warren's 'crude' and 'vulgar' response to opposition to same-sex marriage Klobuchar takes shots at health and education plans supported by Sanders and Warren MORE (D-Mass.) “Pocahontas” during an event honoring Native American Code Talkers “smacks of racism.”

“The reference is using a historic American-Indian figure as a derogatory insult and that’s an insult to all American-Indians,” John Norwood, general secretary of the Alliance of Colonial Era Tribes, told NBC News.

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In a separate statement obtained by ABC News, the president of Navajo Nation, Russell Begaye, said that "in this day and age, all tribal nations still battle insensitive references to our people."

"The prejudice that Native American people face is an unfortunate historical legacy," Begaye said. But he added "the Navajo Nation does not want to engage in this dialogue between Sen. Warren and President Trump."

Trump on Monday honored three Navajos who helped the U.S. Marine Corps develop a secret code during WWII.

"You were here long before any of us were here,” Trump said, standing beneath a portrait of former President Jackson. “Although we have a representative in Congress who they say was here a long time ago. They call her Pocahontas.”

Trump has repeatedly used the derisive nickname when talking about Warren, a reference to her claim of Native American heritage.

Norwood said Trump should “stop using our historical people of significance as a racial slur against one of his opponents.”

Warren also fired back at Trump, saying the event was meant to honor the sacrifice of those in attendance.

“It is deeply unfortunate that the president of the United States can’t even make it through a ceremony honoring these heroes without throwing out a racial slur," she said.

- This story was updated at 5:52 P.M. EST.