President Trump on Monday referred to Sen. Elizabeth Warren (D-Mass.) as "Pocahontas" at an event honoring Native American Code Talkers who served in World War II.

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

Turning to the veterans, Trump said "but do you know what? I like you."

The president made the remark in the Oval Office standing beside three Navajos who helped the U.S. Marine Corps develop a secret code during WWII.

The three Code Talkers did not react to Trump's remark.

Trump has repeatedly used the derisive nickname to refer to Warren, poking fun at her claim of Native American heritage.

"This was supposed to be an event to honor heroes, people who put it all on the line for our country," Warren said later on MSNBC. "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."

But Trump's top spokeswoman defended his comment, saying "Pocahontas" is not a racial slur.

"I think what most people find offensive is Sen. Warren lying about her heritage to advance her career," White House press secretary Sarah Huckabee Sanders told reporters.

Trump during the event also referred to White House chief of staff John Kelly as "chief."

"He's the general and the chief," the president said. "I said, how good were these code talkers? He said, 'Sir, you have no idea. You have no idea how great they were.' "

- This report was updated at 3:37 p.m.