A woman behind a supermarket checkout in the US state of Georgia was shot dead by a customer on Monday in a dispute over wearing a face mask, the local sheriff said.
The customer was then in a gunfight with the shop's security guard, in which they were both wounded. Another cashier, also a woman, was grazed by a bullet.
The violence occurred just after 1pm at the Big Bear Supermarket in DeKalb County, Sheriff Melody Maddox said.
"It was over a mask," Ms Maddox said. "I don't know if they were wearing or not wearing.
"The wearing of the mask and not wearing of the mask, people have their own opinion about it and it is very sensitive at this time."
Several people were inside the store when the confrontation began. The gunman walked out, then returned, pulled out his weapon and shot the cashier.
The security guard opened fire on him, striking him a couple of times, Ms Maddox said.
Businesses in Georgia can request that customers wear a mask to prevent the spread of the Covid-19 virus.
But they are not allowed to insist they do so, according to executive orders issued by Governor Brian Kemp, a Republican.
Ms Maddox did not release the names of the people involved in the shooting.
She said all three were rushed to the hospital, where the guard remains in stable condition after he was shot twice.
The security guard is a retired 30-year veteran of the DeKalb County Police Department who is now a reserve deputy with the DeKalb County Sheriff's Office.
The guard, who works part-time at the supermarket, was wearing a protective vest, Ms Maddox said.