The Danish manufacturer of the building blocks has sent the Utah-based company, Culper Precision, a demand to stop producing the red, blue and yellow covering for handguns.

"Our organization reached out to Lego, which then sent a cease and desist letter to the reckless gun maker," said Shannon Watts, founder of the group Moms Demand Action, which advocates for stricter gun controls.

The colorful brick design gives the semi-automatic weapon a strong resemblance to a Lego toy. The gun maker was marketing it as a "Block19" which sold for between $549 and $765.

"Here's one of those childhood dreams come to life," said Culper Precision in an advert for the gun on Instagram posted on June 24.

"Guns are fun. Shooting is fun. 30 rounds full auto is fun," the company said on its website.

Watts, who stressed that "unintentional shootings have risen by 30 percent in the past year," told the Washington Post her first reaction upon seeing the gun was that it was "sick and children would die."

She said that in 2021 there had been more than 165 accidental shootings by children in the US, according to the organization Everytown. Last year 142 people died as a result of accidental discharges by children or minors, the same group said.

Culper Precision's CEO Brandon Scott confirmed to the Washington Post that he had received Lego's formal notice and said the company had decided to comply, after having sold fewer than 20 of the items.

The controversy comes at a time when President Joe Biden has made the fight against the "epidemic" of gun violence one of his priorities.

The Democratic president presented measures in June to limit the circulation of firearms at the federal level, but Congress is deeply divided on the issue and the Democrats are struggling to push legislation through.