Video has emerged showing teenagers in 'Make America Great Again' hats appearing to mock a Native American man during overlapping marches in the US.
The students, reportedly from the Covington Catholic High School in Kentucky, were in Washington DC to attend the March for Life rally, a yearly gathering of anti-abortion activists.
At the same time, protesters were finishing holding the first Indigenous People's March nearby, which protested injustices against indigenous peoples.
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Video shows Native American and Vietnam veteran Nathan Phillips performing a song of unity as a ceremony to send the spirits home, surrounded by a group of about 60 mostly white students.
In the footage, Mr Phillips steadily keeps singing and beating his drum while one youth stands in front of him, staring into his eyes and smiling.
"This is deep," one young person could be heard saying during his song.
Other teens were whooping, laughing and shouting. Mr Phillips says he heard them chanting "build that wall, build that wall".
"This is indigenous land, you're not supposed to have walls here. We never did for a millennia. Before any of us came here, we never had walls," he said afterwards in a tearful video posted to Instagram.
"We never had a prison. We always took care of our elders, took care of our children, always provided for them, taught them right from wrong."
Defenders of the teens say Mr Phillips was the one who approached them, and they were only being enthusiastic, the Daily Beast reports.
However their actions have been met with widespread condemnation. Left-wing media has accused the students of "smirking" and being "unbearable".
At the same time, the Diocese of Covington and Covington Catholic High School have apologised to March for Life attendees, saying that the teenagers' actions had "tainted" the event and "we will take appropriate action, up to and including expulsion".
"We condemn the actions of the Covington Catholic High School students towards Nathan Phillips specifically, and Native Americans in general," its statement read.
"We extend our deepest apologies to Mr Phillips. This behaviour is opposed to the Church's teachings on the dignity and respect of the human person."
Mr Phillips said he wished he could see the boys' energy put towards "making this country really, really great".