A gunman has killed 10 people, including a police officer, following an hours-long standoff at a grocery store in the US state of Colorado.
Ahmad Al Aliwi Alissa, of Arvada, near Denver, is accused of opening fire Monday afternoon at the King Soopers store in the university city of Boulder, killing people aged between 20- 65, authorities said.
Among the dead was 51-year-old Eric Talley, who was the first police officer to respond to the shooting.
Police took the suspect into custody at the store Monday afternoon, less than an hour after panicked 911 callers told dispatchers of the killings.
The motive behind the Boulder killings -- one of several mass shootings in the US in the last week -- isn't immediately known, and the investigation will take a long time, authorities have said.
"This is a tragedy and a nightmare for Boulder County," the area's district attorney, Michael Dougherty, said.
"These were people going about their day, doing their shopping. I promise the victims and the people of the state of Colorado that we will secure justice."
The incident began at about 14:30 local time (20:30 GMT) on Monday when the suspect entered the supermarket and began firing.
Shoppers and employees of the store said they had to dive for cover or run to safety as the shooting unfolded.
Some of the standoff was captured on camera by a passer-by, showing victims near the grocery store.
US Rep. Gabrielle Giffords of Arizona, who is a shooting survivor, said in a statement. "This is not normal, and it doesn't have to be this way. It's beyond time for our leaders to take action."
The tragedy in Colorado feels especially personal, Giffords said, considering how the shooting she survived outside a Tucson grocery store devastated her community.
Responding to the news, US Senate Democratic leader Chuck Schumer said on Twitter: "This Senate must and will move forward on legislation to help stop the epidemic of gun violence."
President Joe Biden, who has been briefed about the latest attack, said last month he would be recommending tougher legislation to ensure background checks on anyone wishing to purchase a firearm.
The National Rifle Association tweeted on Monday quoting the Constitution's Second Amendment: "A well regulated militia, being necessary to the security of a free state, the right of the people to keep and bear arms, shall not be infringed."
King Sooper is owned by the Kroger company, which said the store will remain closed during the police investigation.
"The entire Kroger family offers our thoughts, prayers and support to our associates, customers, and the first responders who so bravely responded to this tragic situation," the company said via its verified Twitter account.