An American teenager was killed by a man who then posted a photo of his dead body on Instagram, police said.

Bianca Devins, from Utica, New York State, met Brandon Andrew Clark, 21, on Instagram about two months ago, but their relationship has become "intimate, personally," announced the police.

They had met their respective families and spent a lot of time together before attending a concert on Saturday night.

The two men were later disputed and, according to the allegations, in the early hours of Sunday, Clark would have used a large knife to kill the 17-year-old.

Clark's social media followers contacted the police after he had stated that he had killed a person and a picture of Devins's body appeared with the message: "I'm sorry Bianca."

The photos were shared on discussion sites, including 4chan and Discord, where the reaction varied, including calling the police and urging others not to share the photos.

The photo stayed on Instagram for almost 24 hours, according to Buzzfeed.

Published early Sunday morning, Sunday night, it had become blurred and a screen for "sensitive content filtering" was being displayed, which means that someone had reported it as offensive.

But users could still see the photo by touching the screen.

It's only Monday morning that Clark's Instagram account has been disabled.

Brandon Andrew Clark is accused of the murder of Bianca Devins
Picture:
Brandon Andrew Clark is accused of the murder of Bianca Devins

Instagram spokeswoman Stephanie Otway told US media that the account had been disabled for "violating our policies".

She added that the social media company had also "taken steps to prevent others from downloading the content posted on this account again."

The police had found Clark with his vehicle and Ms. Devins' body early Sunday.

He had called the emergency room staff to tell him what he had done and, soon after finding him, he took a selfie with Ms. Devins' body and started stabbing herself.

He was taken to the hospital to undergo surgery, but should recover, police said, adding that he had been charged with second-degree murder.

Devins' family describes her as a "talented artist" and a "wonderful girl, kidnapped too soon".

She had finished her studies last month and was preparing to attend a community college later this year.

"Bianca's smile has lit up our lives," said the family. "We will always remember her as our princess."

Devins, who would have been a "muse" on the TikTok app, had about 6,000 subscribers on Instagram at the time of his assassination, but on Tuesday that number had already surpassed 82,000.