A Dallas-area school board fired a teacher Friday who posted racially charged tweets about the fatal shooting of a black 18-year-old by a white police officer in Ferguson, Missouri.

Duncanville Independent School District trustees unanimously voted to terminate Vinita Hegwood's contract. Hegwood, who is black, has apologized for comments made Nov. 7 on her Twitter account that were laced with expletives and derogatory references to whites and blacks. Administrators have called the remarks "reprehensible."

Hegwood, who taught English at Duncanville High School, was placed on unpaid leave Monday. She apologized in a statement Thursday and submitted her resignation, but the school board rejected a resignation and instead fired her with cause. That doesn't affect a teacher's pension, but it makes him or her ineligible for unemployment benefits, and future employers are told the teacher didn't leave in good standing, school district spokeswoman Lari Barager said.

The tweets were related to the case of Michael Brown, who was unarmed when he was fatally shot Aug. 9. The shooting prompted protests, including some that turned violent, along with ongoing unrest in and around Ferguson, which is just outside St. Louis.

In the apology issued through a teachers union Thursday, Hegwood said she was sorry for "the offensive and unprofessional comments."

"In making those remarks, I was reacting to a series of threatening and racist attacks against me by strangers who disagreed with my expressed opinions on Ferguson, Missouri. I allowed myself to respond emotionally and impulsively," she said.

Barager said that to formally resign, a district employee must submit a letter of resignation and have it approved and signed by the school board.

A phone number for Hegwood couldn't be found in public listings by The Associated Press on Thursday.