Demonstrators hold signs during an El Paso Strong Community Action event in Texas. (Luke E. Montavon/Bloomberg News)

Eight Democratic U.S. senators signed letters on Friday to the chief executives of Google, Amazon and eBay demanding they close the loopholes allowing the sale of firearm accessories on the sites, after a rash of carnage by armed gunmen.

The senators, led by New Jersey’s Robert Menendez, were responding to media reports, including in The Washington Post, that demonstrated how shoppers could easily find ammunition, rifle magazines and other firearm components, in violation of the companies’ own policies. After being contacted by The Post, Google and Amazon removed some of the listings. A Los Angeles Times investigation this week found multiple gun components for sale on eBay, including ones compatible with the AR-15 and AK-47 assault rifles.

“America is in the throes of a gun violence epidemic and it is incumbent upon corporate America to do its part to help end the carnage,” the senators wrote. They asked for details from the companies about how they police their sites, how many postings they’ve eliminated and whether they alert law enforcement about suspicious purchases.

Other senators who signed the letters include presidential candidates Kamala D. Harris (Calif.), Amy Klobuchar (Minn.) and Cory Booker (N.J.).

“Amazon has never allowed guns or ammunition in our store. We require all sellers to follow our selling guidelines and we work hard to keep prohibited products out of our store,” spokeswoman Cecilia Fan said. “In this case, one product was evasively listed and we removed it immediately and took action on the seller.” (Amazon chief executive Jeff Bezos owns The Washington Post.)

Google spokeswoman Caroline Klapper-Matos reiterated a statement provided earlier this week that the sale of weapons, guns and certain gun parts is prohibited and that the company removes such listings when they are discovered.

“EBay is committed to maintaining a safe and trusted marketplace,” eBay spokesman Ryan Moore said. “We take this commitment very seriously and have instituted strict policies and significant resources to prevent illegal firearm parts from being listed on our marketplace.”

The availability online of the gun components highlights the limits of the companies’ software to keep even prohibited items from making their way to the websites. While technology companies constantly update their own software, prohibited goods, language and other behavior often slip through the cracks.

The discovery of gun parts for sale online comes as the nation grapples with three mass shootings in less than a month that left dozens dead or injured. Some Democratic presidential candidates have renewed calls for tighter controls on assault weapon sales, and roughly 40 workers staged a protest outside Walmart’s e-commerce headquarters Wednesday calling for the end of gun sales.

As part of a review of Google’s Shopping site, The Post found boxes of ammunition for sale, as well as gun grips, triggers and rifle magazines with capacity to hold 25 rounds or more. On Amazon, The Post found magazine clips for sale that may have been stored in Amazon’s warehouses, in apparent violation of its policies prohibiting the sale of weapon components.

In Google’s case, some of the listings were available to be purchased using Google as the credit card processor, rather than just directing shoppers to other websites.

“It is not enough to simply ban such sales. Effective monitoring and the suspension of accounts in violation of these policies is essential,” wrote the senators.