BENTONVILLE, Ark. — Wal­mart this month said it would stop selling ammunition that can be used in military-style assault rifles and would call on Congress to increase background checks and consider a new assault rifle ban.

It also said it would discourage its customers from openly carrying guns in its stores. Other retailers, including Walgreens Boots Alliance, CVS Health, Kroger Co. and Wegmans Food Markets Inc., subsequently asked shoppers not to openly carry weapons in their stores.

Walmart’s announcement came a month after a gunman killed 22 people and injured more than two dozen others at a Walmart store in El Paso, Texas.

Four days earlier, a Walmart employee at a store in Southaven, Miss., shot and killed two associates and wounded a police officer.

Doug McMillon, Walmart’s president and chief executive officer, referenced the shootings in a letter to company employees explaining the company’s response.

“In Southaven and El Paso, our associates responded to anger and hate with courage and self-sacrifice. Our immediate priorities were supporting our associates and the impacted families and cooperating with law enforcement. In parallel, we have been focused on store safety and security,” McMillon wrote. “We’ve also been listening to a lot of people inside and outside our company as we think about the role we can play in helping to make the country safer. It’s clear to us that the status quo is ­unacceptable.

“After visiting El Paso on August 6, I mentioned that we would be thoughtful and deliberate in our responses. We’re ready to share our next steps. We’ve been giving a lot of thought to our sale of firearms and ammunition. We’ve previously made decisions to stop selling handguns or military-style rifles such as the AR-15, to raise the age limit to purchase a firearm or ammunition to 21, to require a ‘green light’ on a background check while federal law only requires the absence of a ‘red light,’ to videotape the point of sale for firearms, and to only allow certain trained associates to sell firearms. Today, we’re sharing the decisions we’ve made that go further.”

The policy change takes effect immediately, McMillon said, with stores ceasing to offer those products after selling through existing inventories. The retailer stopped selling handguns in all U.S. stores except those in Alaska over two decades ago but will now cease such sales in that state as well.

“We know these decisions will inconvenience some of our customers, and we hope they will understand. As a company, we experienced two horrific events in one week, and we will never be the same,” he said. “Our remaining assortment will be even more focused on the needs of hunting and sport shooting enthusiasts. It will include long-barrel deer rifles and shotguns, much of the ammunition they require, as well as hunting and sporting accessories and apparel. We believe these actions will reduce our market share of ammunition from around 20% to a range of approximately 6% to 9%.”

McMillon said there had been “multiple incidents” since the El Paso massacre where “individuals attempting to make a statement and test our response have entered our stores carrying weapons in a way that frightened or concerned our associates and customers. We have also had well-intentioned customers acting lawfully that have inadvertently caused a store to be evacuated and local law enforcement to be called to respond.”

Walmart will provide signage to signal its new approach to shoppers who bring guns into stores. “We will treat law-abiding customers with respect, and we will have a very nonconfrontational approach. Our priority is your safety,” McMillon wrote in his letter to associates.

“Finally, we encourage our nation’s leaders to move forward and strengthen background checks and to remove weapons from those who have been determined to pose an imminent danger,” McMillon wrote.

“We do not sell military-style rifles, and we believe the reauthorization of the Assault Weapons ban should be debated to determine its effectiveness. We must also do more, as a country, to understand the root causes that lead to this type of violent behavior,” he said. “Today, I’m sending letters to the White House and the congressional leadership that call for action on these commonsense measures.”