Image copyright Getty Images Image caption Kyle Kashuv has become a gun rights activist since the attack on his Florida high school

A teenager who survived a gun massacre at his Florida high school has said he lost his spot at Harvard University over past racist remarks.

Kyle Kashuv, 18, said the online comments were made when he was 16, and were done "in an effort to be as extreme and shocking as possible".

He had since apologised and on Monday shared what appeared to be a rescission letter from the university.

Seventeen students and faculty were killed in Parkland, Florida in 2018.

"Harvard deciding that someone can't grow, especially after a life-altering event like the shooting, is deeply concerning," he posted in a thread to his 300,000 Twitter followers.

"If any institution should understand growth, it's Harvard, which is looked to as the pinnacle of higher education despite its chequered past," he wrote, adding: "Throughout its history, Harvard's faculty has included slave owners, segregationists, bigots and anti-Semites."

"If Harvard is suggesting that growth isn't possible and that our past defines our future, then Harvard is an inherently racist institution. But I don't believe that."

A spokeswoman for Harvard told CNN on Monday that the university does "not comment publicly on the admissions status of individual applicants".

Media playback is unsupported on your device Media caption How much do US students fear school shootings?

Since the shooting, Mr Kashuv has stood apart from his peers at Marjory Stoneman Douglas High School by calling for private gun rights to be protected under the US constitution's second amendment. Many of the Parkland shooting survivors have focused their efforts on gun control in the wake of the shooting.

Classmates David Hogg and Jaclyn Corin - who called for more restrictions on gun sales after surviving the massacre - are due to begin their study at Harvard, one of the most prestigious schools in the US, in 2020.

What happened?

In May the high school senior apologised for the comments, which were made in text and Skype messages as well as in a shared Google document for a class study guide two years ago.

Screenshots of those remarks were shared online by at least one of Mr Kashuv's classmates, Ariana Ali, who told the New Yorker: "The more prominent he got, the more I was bothered by his hypocrisy."

On Monday Mr Kashuv took to Twitter to say "we were 16-year-olds making idiotic comments, using callous and inflammatory language in an effort to be as extreme and shocking as possible", and added that he "immediately apologised" for the two-year old exchanges.

"I'm embarrassed by it, but I want to be clear that the comments I made are not indicative of who I am or who I've become in the years since."

The alleged comments included threats against Jews and racial slurs in reference to African Americans.

In one message he apparently wrote he would "make a CSOG map of Douglas [high school] and practise". Some students claimed the reference was to the shooting-themed video game "Counter-Strike: Global Offensive".

Media playback is unsupported on your device Media caption Zachary Cruz: 'My brother was the Parkland gunman'

Mr Kashuv said he turned down scholarships from other universities and the deadline to accept other offers has passed.

Harvard University - like many other US colleges - reserves the right to rescind admission offers under certain instances, including if students' grades drop at the end of high school or if they engage in questionable behaviour.

The Ivy League college revoked offers for 10 prospective students in 2017 over explicit and racist messages shared in a private Facebook group, according to the Harvard Crimson school newspaper.