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A Catholic diocese outside Cincinnati is investigating the actions of some of its high school students during the Indigenous Peoples March in Washington on Friday.

Some students wearing Make America Great Again hats and clothing appeared to surround and may have taunted a Native American troupe as it performed the "American Indian Movement" song about strength and courage. It's not clear which of those young people surrounding the Native Americans are students of Covington Catholic High School in Covington, Kentucky. There appears to have been jeering by another group of people preceding the incident recorded on video.

But the Diocese of Covington criticized any students who participated in the action, which broke out as a group from the school was in Washington for the March for Life, an anti-abortion event.

Its statement, forwarded by Laura Keener, a spokeswoman for diocese, singled out Nathan Phillips, an Omaha tribal elder. In social media videos of the incident Phillips can be seen singing as a male taunts him smilingly and gets close to his face.

The male was not identified.

"We condemn the actions of the Covington Catholic High School students towards Nathan Phillips specifically, and Native Americans in general, Jan. 18, after the March for Life, in Washington, D.C.," the diocese's statement reads. "We extend our deepest apologies to Mr. Phillips. This behavior is opposed to the Church's teachings on the dignity and respect of the human person."

The diocese said that the matter was under investigation and that students could be expelled.

Asked for comment by NBC News, the interim head of the Vatican press office, Alessandro Gisotti, said the Diocese of Covington had already "strongly condemned" the students' actions.

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During the incident, some young people appeared to surround Native Americans and others started to jump and chant. A young person is heard saying during the Native Americans' song, "This is deep."

In an interview with MSNBC's Joy Reid on Sunday, Phillips said he approached the group of students after having witnessed them going back and forth with a group known as the Black Hebrew Israelites.

Phillips said the students surrounded the significantly smaller group as participants of the Indigenous People's March watched on the sideline.

Drumming and praying to God to help end the march on a positive note, Phillips approached the rivaling groups in hopes of defusing the situation, he said.

"Look at my America. Look at my black and white brothers here. They’re tearing at each other. We are at a point where you can't stand by and watch this," Phillips said.

Phillips told NBC News that some of the young people surrounding him chanted support for President Donald Trump's proposal to build a wall along the U.S.-Mexico border.

"Chants of 'build the wall' and other things that were even worse," he said as he stood in the rain in Washington. "They were brought up to believe I'm less than human."

Phillips said he has getting hateful phone calls and is afraid to answer his phone in the wake of the incident, which came nearly a week after Trump mocked a claim by Sen. Elizabeth Warren, D-Mass., to Native American ancestry.

If Elizabeth Warren, often referred to by me as Pocahontas, did this commercial from Bighorn or Wounded Knee instead of her kitchen, with her husband dressed in full Indian garb, it would have been a smash! pic.twitter.com/D5KWr8EPan — Donald J. Trump (@realDonaldTrump) January 14, 2019

"I'm still trying to process it," Phillips said. "Who they were, who those young folks were, where they came from and who's bringing them up. Where were the chaperones? How did this come to this point? ...

"It's goinga take us all to come together," he added. "I'm about prayer, but then you have to have some action to go with it."

Phillips said Sunday that he does not know whether the boy in the video should be expelled from school, but he said the trip's chaperones should be fired.

"Where were they? How did they allow these students to come to this point after an hour of this happening? Were they with them? Were they encouraging them?" he asked.

Rep. Debra Haaland, D-N.M., who with Sharice Davids, D-Kan., became the first Native American women elected to Congress, said the video and the growing intolerance made her "really sad."

"These young kids should be taught to respect their elders, that they're important," Haaland said. "People ... they're getting so bold with what they're saying."

CORRECTION (Jan. 19, 2019, 5:40 p.m. ET): An earlier version of this article misidentified the Diocese of Covington. It is a diocese, not an archdiocese.

CORRECTION (Jan. 24, 2019, 8:40 a.m. ET): An earlier version of this article misstated Nathan Phillips' military record. He served in the Marines but was not deployed to Vietnam.