A federal grand jury has indicted a man for leaving voice mails in which he vowed to assault and murder Rep. Diane Black, in a case that marks the third instance of a lawmaker going public about death threats within the past month.

The man, Clifton Ward, left voice mails threatening Black (R-Tenn.) in May and June, according to the indictment, which was filed June 26.

Black, who is in the final leg of a heated gubernatorial primary in Tennessee, declined to describe the content of the voice mails in an appearance on Fox News this week, saying only that they “were threatening enough that they concerned the police.”

“I can’t talk about the details except to say that they were threats, and they were serious enough threats that the grand jury did take action,” Black told Fox News on Wednesday. “This is not the first time, and it probably won’t be the last time that when people get angry, they do and say things that are threatening.”

Eva Malecki, a Capitol Police spokeswoman, said the department does not comment on ongoing investigations.

Amid an increasingly hostile political environment, reports of death threats against lawmakers have been on the uptick.

This month, Sen. Rand Paul (R-Ky.) said a man was arrested after threatening to kill him and his family with an ax. Just a few days earlier, Rep. Maxine Waters (D-Calif.) announced that she had canceled events in Texas and Alabama after a “very serious death threat” was made against her.

Asked during her Fox News appearance what she believes to be driving such threats, Black said, “I think sometimes the rhetoric just gets people so stirred up.”

“When there are these radical statements made and insinuations that would be physical, I think it does gin people up,” she said. “And it’s unfortunate because that is not what at all our dialogue should be about.”

House Majority Whip Steve Scalise (R-La.), who was critically injured after a gunman opened fire at a congressional baseball practice last year, condemned the threats against Black and said that such actions must come to an end.

“I’m glad my friend, @RepDianeBlack, was not harmed,” Scalise said in a tweet Thursday. “These threats of violence have to stop. They are not an acceptable way to express political disagreements.”