The Orange County School District said in a statement seen by news media that "a teacher gave an inappropriate assignment about school violence... (and) has been terminated." It provided no further detail.

Jeffrey Keene, a veteran teacher who was hired at Dr. Phillips High School in Orlando in January, told a local Fox subsidiary that he was dismissed without explanation.

An apparent copy of the assignment posted by Keene on Facebook shows that he had asked his upper grade students to imagine, as part of a psychology lesson, that "today was your 'last day' alive" and write their own death notices.

He further asked students to think about "why the United States is having so many mass shootings," and to consider "what kind of 'positive actions' can we... take to 'decrease the number of mass shootings?'"

A disclaimer at the bottom of the assignment says it is in "no way" intended to upset anyone, though Keene said some students apparently complained to school counselors.

Keene, 63, told Fox that his challenge to students was to "get rid of all the fluff and show them what's important in the world."

"If you can't talk real to (the students), then what's happening in this environment?" Keene asked. "In my mind, I've done nothing wrong."

He told Fox that he planned to appeal the decision, though as a probationary teacher not yet a member of the teachers' union he has less leverage to do so.

Orlando was the site of one of the country's deadliest mass shootings -- the June 2016 assault by a 29-year-old gunman at the Pulse nightclub that killed 49 people.

One of the worst US school shootings occurred a few hours' drive south, in the Miami suburb of Parkland, when a 19-year-old shooter killed 17 people in 2018.

Gun violence -- and what to do about it -- is a deeply divisive issue in the United States. Two state legislators in Tennessee were recently expelled from the assembly after interrupting debate to demand gun control measures.