The U.S. Justice Department said on Wednesday it has charged a Missouri man for leaving threatening voicemails for an election official in Arizona, marking the sixth federal criminal case brought so far to combat the rising tide of threats against local election officials.

Walter Lee Hoornstra, 50, of Tecumseh was charged in an indictment handed down on Tuesday with one count of communicating an interstate commerce threat and a second count of making a threatening phone call.

The indictment alleges that Hoornstra left a voicemail on a Maricopa County election official's personal cell phone saying: "You call things unhinged and insane lies when there's a forensic audit going on. You need to check yourself. You need to do your [expletive] job right because other people from other states are watching your ass. You [expletive] renege on this deal or give them any more troubles, your ass will never make it to your next little board meeting."

The indictment did not identify which official in Maricopa County, Arizona's most populous county, was the target of the threats.

Last year, the Justice Department launched an election threats task force. The increase in threats coincided with false claims by former Republican President Donald Trump that the 2020 election had been stolen due to widespread voter fraud.

In the 2020 election, Arizona was one of the key battleground states. President Joe Biden carried Maricopa County by about 45,000 votes, making it crucial to his narrow victory.

Election officials in Maricopa County later refuted a partisan audit run by Trump's allies and carried out by a private company called Cyber Ninjas which tried to cast doubt on Biden's win.

In an investigative series published last year, Reuters documented more than 850 threats and menacing messages to U.S. election workers.

Since the task force was launched, the Justice Department has reviewed more than 1,000 contacts reported as hostile or harassing by the election officials and volunteers.

Of those, about 11% have met the legal standards necessary to launch a federal criminal investigation.

The identity of Hoornstra's lawyer could not immediately be determined. If convicted on both counts, Hoornstra could face up to seven years in prison.