A diocese in Kentucky apologized Saturday after videos emerged showing students from a Catholic boys' high school mocking Native Americans outside the Lincoln Memorial after a rally in Washington.

The Indigenous Peoples March in Washington on Friday coincided with the March for Life, which drew thousands of anti-abortion protesters, including a group from Covington Catholic High School in Park Hills.

Videos circulating online show a teen staring at and standing extremely close to Nathan Phillips, a 64-year-old Native American man singing and playing a drum.

"I was sad for him. I was really, truly sad for him," Phillips said in an interview with NBC News.

"The actions that he was involved in, you know, who allows the children to treat others that way? Who teaches our children that? What was in their minds? You know, chants of 'build the wall' and other things that were even worse."

Other students, some wearing Covington clothing and many wearing "Make America Great Again" hats and sweatshirts, apparently chanted, laughed and jeered.

"I was scared. I was afeared. But - no buts - we have to stand strong," Phillips told NBC News.

Another encounter apparently took place before the one went viral.

In a joint statement, the Roman Catholic Diocese of Covington and Covington Catholic High School apologized to Phillips. Officials said they are investigating and will take "appropriate action, up to and including expulsion."

"We extend our deepest apologies to Mr. Phillips," the statement read. "This behavior is opposed to the Church's teachings on the dignity and respect of the human person."

Asked for comment by NBC News, the interim director of the Holy See Press Office, Alessandro Gisotti, said that the “diocese [of Covington] has already strongly condemned” the students’ actions.

According to the "Indian Country Today" website, Phillips is an Omaha elder and Vietnam veteran who holds an annual ceremony honoring Native American veterans at Arlington National Cemetery.

In an interview with the Washington Post, Phillips said he felt threatened by the teens. “It was getting ugly, and I was thinking: ‘I’ve got to find myself an exit out of this situation and finish my song at the Lincoln Memorial,’ ” he said. “I started going that way, and that guy in the hat stood in my way and we were at an impasse. He just blocked my way and wouldn’t allow me to retreat.

Phillips said he kept drumming and singing, focusing on his wife, who died of bone marrow cancer, and threats to indigenous communities around the world. “I felt like the spirit was talking through me,” he said.

In a video posted to Instagram, Phillips wiped away tears. "When I was there singing, I heard them saying 'Build that wall, build that wall,'" Phillips said. "This is indigenous lands. We're not supposed to have walls here. We never did."

He said he wished the group would put their energy into "making this country really great."

Phillips said the incident started as the students from Covington Catholic were observing a group of Black Israelites talk, and started to get upset at their speeches, according to Cincinnati.com.

Phillips said some of the members of the Black Hebrew group were also acting up, "saying some harsh things" and that one member spit in the direction of the Catholic students.

Chase Iron Eyes, a spokesman for the Indigenous Peoples March and an attorney for the Lakota People's Law Project, told the Courier Journal Saturday that Phillips initially approached the students in an attempt to defuse a situation. Chase Iron Eyes said Phillips was swarmed though some video posted on social media seems to show Phillips walking into the crowd of students.

State Rep. Ruth Buffalo, a North Dakota state lawmaker and member of the Mandan, Hidatsa and Arikara Nation, said she was saddened to see students showing disrespect to an elder who is also a U.S. military veteran at what was supposed to be a celebration of all cultures.

"The behavior shown in that video is just a snapshot of what indigenous people have faced and are continuing to face," Buffalo said.

She said she hoped it would lead to some kind of meeting with the students to provide education on issues facing Native Americans.

The videos prompted a torrent of outrage online. Actress and activist Alyssa Milano tweeted that the footage "brought me to tears," while actor Chris Evans tweeted that the students' actions were "appalling" and "shameful."

U.S. Rep. Deb Haaland, D-New Mexico, who is a member of the Pueblo of Laguna and had been at the rally earlier in the day, used Twitter to sharply criticize what she called a "heartbreaking" display of "blatant hate, disrespect, and intolerance."

Haaland, who is also Catholic, told The Associated Press she was particularly saddened to see the boys mocking an elder, who is revered in Native American culture. She placed some of the blame on President Donald Trump, who has used Indian names like Pocahontas as an insult.

"It is sad that we have a president who uses Native American women's names as racial slurs and that's an example that these kids are clearly following considering the fact that they had their 'Make America Great Again' hats on," Haaland said. "He's really brought out the worst in people."

CORRECTION (Jan. 23, 4:07 p.m. ET): The Associated Press reported that Indian Country Today said the Native American, Nathan Phillips, was a Vietnam veteran. Military records show that he served in the U.S. Marine Corps but did not serve in Vietnam.