President Joe Biden has called for an assault weapon ban and the closure of background check loopholes, after the seventh mass killing this year in the US left 10 dead.

In an address to the nation following the bloodshed at a supermarket in Colorado, the president said simply: “We must act.”

And he called on political colleagues of all parties to support him.

He said he “does not need to wait another minute to take common sense steps to save lives in the future” and said gun control measures should not be a partisan issue.

He made a plea for a ban on both assault weapons and high-capacity magazines and called for the closing of loopholes in the current background check systems that are carried out when a person buys a gun.

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Ten people killed in Colorado shooting

On Monday, SWAT teams and at least three helicopters were called to the King Sooper store in Boulder – about 28 miles north of central Denver – after reports of a man wearing tactical gear shooting a rifle inside.

Terrified shoppers and workers scrambled for safety while armed officers exchanged fire with the suspect.

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Police officer and father of seven Eric Talley, 51, ran to the store following the call – but was killed as he tried to stop the man.

Nine other members of the public, mostly doing their grocery shopping, were also shot dead.

Ahmad Al Aliwi Alissa, a 21-year-old from Arvada, Colorado, has been charged with 10 counts of murder. He is currently in hospital in a stable condition, police said, and is expected to be released and transported to Boulder County Jail later on Tuesday.

The attack was the seventh mass killing this year in the US, following last week’s shooting that left eight people dead at three Atlanta-area massage businesses.

Just hours after the horror unfolded in Boulder, the National Rifle Association again defended the right to gun ownership by tweeting a photograph of the Second Amendment to the Constitution with the caption: “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.”

President Biden’s plea comes as Senate Democrats say they are pushing toward a vote on expanded gun control measures, although prospects for any major reform are dim, for now, in the closely divided Congress.

Senate majority leader Chuck Schumer vowed to bring to the floor legislation passed by the House that would require background checks for most gun sales and transfers.

He said the Senate “must confront a devastating truth” after a lack of Congressional action on the issue for almost three decades.

White House flags will again be flown at half mast – only hours after they were raised having been lowered for Atlanta’s victims.

The names of those who died in Boulder were read out at a news conference on Tuesday: Denny Strong, 20, Neven Stanisic, 23, Rikky Olds, 25; Tralona Bartkowiak, 49, Suzanne Fountain, 59, Teri Leiker, 51, Kevin Mahoney, 61, Lynn Murray, 62 and Jody Waters, 65.

Investigators said they were confident Alissa had acted alone, though they did not offer any details on what might have motivated the massacre.

“It would be premature for us to draw any conclusions at this time,” Michael Schneider, the agent in charge of the FBI’s field office in Denver, said at the news briefing.

Vice President Kamala Harris described the Boulder shooting as “absolutely baffling” and paid tribute to the victims who were “living their lives, not bothering anybody”.

Investigators have started sorting through evidence and witness interviews and do not yet have details on a motive for the shooting.

Dean Schiller told the Associated Press he had just left the supermarket on Monday when he heard gunshots and saw three people lying face down, two in the car park and one near the doorway.

He said he “couldn’t tell if they were breathing”.

Video posted on YouTube showed one person on the floor inside the store and two more outside on the ground. What sounds like two gunshots are also heard at the beginning of the video.