Google has banned gun sales from its new shopping platform, a move drawing fire from hunters and weapons enthusiasts but praised by gun control activists.

Google made the change May 31 when it transformed its "product search," which had consisted of free listings, into "Google Shopping," which has paid listings and is governed by the tech giant's advertising policies.

In its shopping service, Google "doesn't allow the promotion of weapons or devices designed to cause serious harm or injury," the website said, describing its advertising policies.

The ban includes "guns, gun parts or hardware, ammunition, bombs, knives, throwing stars, and brass knuckles," it said.

Even though the policy was announced more than a month ago, it drew notice only in recent days after it was pointed out by a blog called Outdoor Hub, dedicated to "outdoor enthusiasts."

Blog contributor Edward Pierz said Google "censors" firearm searches, and linked to a petition to "Tell Google not to interfere with our 2nd amendment rights," a reference to the constitutional right to bear arms.

"If you wish to purchase a gun, you are required to do a background check and utilize an FFL (federal firearms license) holder to make the purchase regardless of whether you buy it online or through a gun shop," the petition says.

"The new policy will only effectively disable many law abiding citizens from acquiring legal weapons for legitimate purposes at reasonable prices, and hurt many many small business's income."

Other gun rights activists also poured criticism on the California tech giant.

A National Rifle Association statement said Google "has adopted a new and discriminatory policy with respect to the advertising of firearms, ammunition and related products."

"This appears to be a calculated political statement by Google at a time when most other large online retailers and search services are increasing the level of information they provide and the number of gun-related products they offer for sale," the NRA said.

"Fortunately, with so many other options available to consumers, Google's attempt to limit information about legal and constitutionally protected products will likely prove futile."

But Daniel Vice, senior attorney at the Brady Center to Prevent Gun Violence, welcomed the move.

"We applaud Google for acting to restrict sales of dangerous weapons that would frequently occur without background checks," Vice told AFP.

"The Internet is a notorious source of guns for killers.

Vice said one recent study by Mayors Against Illegal Guns showed 62 percent of online gun sellers were willing to sell weapons to people who could not pass a background check.

"It's so easy online to find guns and buy them without a background check, so Google's policy is more than reasonable," he said.

Bloggers in favor of gun rights were sharply critical, however.

On the Texas Bowhunter blog, one contributor wrote: "Google is shooting themselves in the foot (pun intended). I guess they won't mind the govt's attempt at censoring the Internet... 'in the interest of consumer safety.'"

A Google spokeswoman declined to comment on the reasons for the policy. She said guns may show up on "an organic search" but not in shopping searches.

But the Shopping policies point out that Google "has a strong culture and values, and we've chosen not to allow ads that promote products and services that are incompatible with these values."

Matt McGee of the tech blog Search Engine Land said the change "certainly seems to be within Google's rights."

But he added it "seems like a slippery slope to use vague terms like 'culture and values' to determine who can and can't list products in Shopping Search -- a slope that's likely to open Google up to further criticism if it continues to apply that principle to other industries."