A 25-year-old bank employee opened fire at his workplace Monday in Louisville, in the US state of Kentucky, killing five people and wounding at least eight others in a livestreamed attack before police shot and killed him.

After an initial death toll of four, Louisville authorities announced in the evening that a fifth victim, a 57-year-old woman, had died of her injuries.

Police identified the gunman in the latest US mass killing as a white man named Connor Sturgeon and said he was an employee of Old National Bank, located downtown in Kentucky's largest city.

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After receiving reports of gunfire in the bank at 8:38 am (1238 GMT), police were on the scene within three minutes. The suspect shot at officers, who returned fire and killed him, interim police chief Jacquelyn Gwinn-Villaroel told an afternoon press conference.

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"His weapon of choice was a rifle," she said without specifying if it was an assault weapon of the kind often used in the massacres that have become tragically common in the United States.

Gwinn-Villaroel confirmed that the shooter, whose age was at first reported as 23 but later updated by police to 25, had broadcast live video of the attack on Instagram.

A spokesperson for Meta, the social media app's parent company, told AFP that it was "in touch with law enforcement and quickly removed the livestream of this tragic incident this morning."

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There was no immediate word on the suspect's motive, but CNN cited a law enforcement source as saying he had just been informed he was losing his job.

Gwinn-Villaroel said that three people were in critical condition, including a police officer who took a bullet to the head.

One of those victims later succumbed to her injuries, the Louisville Police Department said, adding to another woman and three men killed in the attack -- all aged between 40 and 64 years old.

One of the men killed, Tommy Elliot, 63, was a friend of the Louisville mayor and of the Democratic governor of Kentucky. The latter said he once ran a campaign out of the building where the shooting took place.

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"Tommy Elliott helped me build my law career. Helped me become governor. Gave me advice on being a good dad," Andy Beshear told the news conference, visibly shaken.

"He was an incredible friend," the governor said.

This was the latest spasm in a gun crisis that has left more than 4,900 people dead of firearm-related violence already in 2023, according to the Gun Violence Archive.

President Joe Biden -- who is pushing for lawmakers in Washington to break a years-long deadlock and take action against gun violence -- voiced frustration after the latest "senseless" killings.

"Too many Americans are paying for the price of inaction with their lives," Biden wrote on Twitter, adding: "When will Republicans in Congress act to protect our communities?"

The White House later said that Biden had spoken by phone with Beshear.

- Windows 'blown out' -

The incident triggered a massive police deployment outside the Old National Bank building.

CNN reported that some people had been able to take refuge in the bank vault and lock themselves in -- contacting police from inside.

Fox affiliate WDRB cited a witness saying she heard multiple gunshots and breaking glass while in her car at an intersection near the site.

"Gunfire erupted, like, right over my head," said the woman, who gave her name only as Debbie. "When I turned, I saw that one of the windows in the bank had been blown out," she added.

The United States, a country of around 330 million people, is awash with some 400 million guns, and deadly mass shootings are a regular occurrence.

Efforts to tighten gun controls have for years run up against opposition from Republicans, staunch defenders of the constitutional right to bear arms. The political paralysis endures despite widespread outrage over recurring shootings.

In the latest illustration of the deadlock, two Tennessee lawmakers were expelled from the state legislature last week after staging a floor protest calling for tougher gun control, in the wake of a deadly shooting at an elementary school in Nashville.

Monday's mass shooting in Louisville was the 146th of the year according to the Gun Violence Archive -- which defines such acts as incidents in which four or more people were shot or killed, excluding the assailant.