Oklahoma City, Oklahoma - The US Education Department is opening an investigation into an Oklahoma school district where a nonbinary student died a day after clashing with three other students in school.

In a letter sent Friday to the Human Rights Campaign – the largest LGBTQIA+ political lobbying organization in the United States – the department said the probe would assess whether the district had failed to respond appropriately to "sex-based harassment."

The student, a 16-year-old named Nex Benedict who identified as Two-Spirit and non-binary, was in an altercation with three girls in a restroom in their high school in the city of Owasso on February 7, witnesses and the student's mother said.

Benedict was seen by a school nurse but was sent home.

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Police were not contacted until Sue Benedict, the student's mother, phoned later in the day from a hospital emergency room.

In a video released by police, Nex Benedict told police from a hospital bed that Nex had poured water on three girls after being mocked over "the way that we dress... All three of them came at me."

Sue Benedict told police that Nex had been "jumped" by the three, adding, "I'm furious that the school just kind of said, 'Come get your kid.'"

The following day Nex Benedict fell ill at home, was rushed back to the hospital, and died.

Sue Benedict and others told local media that her child had been bullied by fellow students for more than a year.

Body cam footage shows Benedict telling police after the incident they did not know the girls, although the attackers had previously made fun of the way the 10th grader and their friends dressed.

Benedict was reportedly talking with their friends in the bathroom when the girls made a disparaging comment about the way they laughed. Benedict responded by pouring water on the girls.

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The teen told police officers, "They got my legs out from under me and got me on the ground and started beating the s*** out of me."

No cause of death has yet been formally determined, but the case has sparked outrage from LGBTQIA+ advocacy groups.

Oklahoma has a law prohibiting students from using bathrooms not in alignment with their sex at birth.

The school district said in a statement that there had been "speculation and misinformation" about the altercation, and it noted that the fight was brief and that all those involved had walked under their own power to a nurse's and an assistant principal's office.

Over 350 organizations supporting LGBTQ+ rights sent a letter to Oklahoma Legislature leaders this week calling for the immediate removal of the state's schools Superintendent Ryan Walters.

The White House also responded to the "devastating" event, saying, "Our hearts are with Nex Benedict's family, friends, entire school community in the wake of this horrific and gut-wrenching tragedy."

They urged people looking for support with similar issues to phone a help line dedicated to serving LGBTQ+ people: calling 988 and dialing 3.