Twenty-nine people were killed and dozens injured in two shootings in Texas and Ohio, officials say.
Hours after 20 people were killed in a mass shooting in El Paso, Texas, a gunman killed 9 others in Dayton, Ohio.
The police managed to arrest the Texas bomber. But the Ohio bomber was shot dead by security personnel who were near the site of the accident.
And local media in Ohio quoted eyewitnesses as saying that the gunman tried to enter a bar, but opened fire outside it when he was arrested.
Dayton Police said the motives for the shooting remained unknown, and that they were investigating the incident, in which 16 people were injured.
Texas Governor Greg Abbott described the attack in his state as “one of the bloodiest days in Texas history”.
The accident, which injured 26 others, took place at a branch of Walmart supermarket, near the Silo Vista mall, a few miles from the US-Mexico border.
The authorities arrested a 21-year-old suspect, who is believed to be the only one involved in the shooting.
US media reported that the suspect’s name was Patrick Croeseus, and that he was a resident of the Dallas area, about 650 miles east of El Paso.
Media outlets broadcast CCTV footage, said to be the militant, showing a man wearing a dark shirt and earphones branding an assault rifle.
Police said they did not believe there was an imminent threat to the public, but they were still conducting searches.
US President Donald Trump called the attack a “cowardly act.”
“I know that I stand with everyone in this country to condemn the hate act that took place today. There are no reasons or arguments that justify the killing of innocent people,” he said on Twitter.
El Paso Police Chief Greg Allen said that reports of a gunman firing came at 10:39 local time (16:39 GMT), and that police had reached the site within six minutes.
The store was full of shoppers, as people flocked to buy school supplies.
Earlier, the police announced, in a tweet, that there is an “urgent need” to donate blood.
“People were terrified and running,” one of the eyewitnesses, Qianna Long, told Reuters, adding that she and her husband, among other shoppers, took shelter in a storage room.
Another witness, Glendon Oakley, told CNN that he was in a sports supplies store inside the nearby Selo Vista mall when a child rushed inside and “told us there was someone shooting at Walmart.” He added, “No one took what the child said seriously,” but only minutes later he heard the sounds of gunshots, and then all he thought was “keeping the children away.”
Another witness who was in the shopping center told CBS News, “Employees told me that they heard gunshots and that people were trying to enter the store to take cover. I was trying to stay calm, but I was shivering.”