WASHINGTON (AP) — The number of threats targeting federal judges has more than doubled over the last three years amid a surge in violent and harassing messages directed at public officials around the U.S., the head of the U.S. Marshals said in congressional testimony Wednesday.

Threats to prosecutors and other court staff have shown a similar alarming increase, Marshals Director Ron Davis said during a House committee hearing.

"Core to our democracy is an independent judiciary that can operate safely without the threat of violence," Davis said. "The current and evolving threat environment facing the judiciary constitutes a substantial risk to our democracy."

In 2023, the Marshals investigated 457 threats against federal judges, compared to 224 in 2021. Threats to prosecutors have also more than doubled during that time frame, according to data provided by the U.S. Marshals. The agency is tasked with safeguarding more than 2,700 federal judges.

They include threats to kill federal judges and carry out mass shootings at courthouses, Davis said.

There's also been a rise in judges and court officials being targeted on social media, and a "troubling increase," in swatting, or fake 911 calls aimed at provoking a police response, he said.

Court officials targeted recently include judges and prosecutors overseeing the criminal cases against former president Donald Trump. In 2022, shortly after the leak of a draft opinion overturning Roe v. Wade, a man was stopped near the home of Justice Brett Kavanaugh with weapons and zip ties.

Davis' warning comes as politicians, state capitols and election officials are increasingly targeted by graphic threats, bomb scares and fake emergency calls.