An Arizona police officer has been accused of threatening Democratic Phoenix Mayor Kate Gallego, who has since been assigned additional security.

The Phoenix Police Department released a statement Tuesday that didn't directly confirm the threat but noted that an investigation into "claims of misconduct" was underway and an officer had been asked to remain at home.

"The Phoenix Police Department takes claims of misconduct by its officers seriously," Sgt. Mercedes Fortune wrote.

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Neither the Phoenix Police Department nor Gallego's office immediately responded to requests for comment from Fox News.

Fortune said the department's Professional Standards Bureau is set to conduct the internal investigation of the matter, while a criminal inquiry will be spearheaded by the Tempe Police Department.

"The Mayor's office is aware of the investigation and steps have been taken to ensure Mayor Gallego’s safety," wrote Fortune.

The Tempe Police Department confirmed in its own statement that it had opened a criminal investigation on Friday, Oct. 23. 

While the officer was not identified by either Mayor Gallego's office or Phoenix police, FOX 10 Phoenix reportedly reached out to the officer in question who did not wish to comment.

ABC15 Arizona said fellow officers initially reported the threat.

This is not the first time a Phoenix mayor has received threats: Democrat Phil Gordon, who was elected in 2003, started receiving death threats in 2010.

"Some people don't want to hear what I'm saying," Gordon told reporters. 

Gordon spoke out against then-Maricopa County Sheriff Joe Arpaio on illegal immigration and opposed an Arizona law that made it illegal not to carry immigration papers and allowed officers to detain any individual suspected of being in the country illegally.

Gordon hired 24/7 security after receiving threatening emails, texts and phone calls, and one officer who was with him was stabbed with a knife, according to FOX 10. 

This year, Gallego is one of three candidates in the November mayoral election. She's running against Republican Merissa Hamilton and fellow Democrat Tim Seay. She has, notably, pushed for police reforms, including a citizen review board. 

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According to Gallego spokeswoman Jeanine L'Ecuyer, the threat came within the past two weeks. L'Ecuyer said that additional police protection had been provided to the mayor.