Image copyright Groupon/Twitter Image caption The offensive adverts have been removed

Groupon, the online discounter, says it is "appalled" that a racial slur was used to sell footwear on their website.

Customers noticed on Wednesday an offensive epithet aimed at black people was used to describe a shade of brown available for some footwear.

Several social media users pledged to boycott the Chicago-based company over the advertisements.

Groupon says the adverts for two different brands of boots originated with a "third-party seller".

The pages describing the boot's colour as "[n-word] brown" were taken down, but several outraged online users took screenshots and reposted them.

The pair of "Women's Fringed Suede Moccasin Boots" and "Men's Suede Leather Fur Lining Winter Boots" both offered the colour as a purchase option.

"We are appalled that this language was displayed on our site," Bill Roberts, the vice-president of Global Communications for the company, told US media.

Image copyright Twitter/Groupon

"This product description was provided by a third-party seller via our self-service platform," his statement continued.

"Regardless, this is completely unacceptable and violates our policies - to say nothing of our values."

Mr Roberts added that the seller has now been "removed" from Groupon.

"Language like this has no place on Groupon, and we're further strengthening our self-service controls to ensure it doesn't happen again," the statement concluded.

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A number of Twitter users said they would no longer give their business to the website.

"I will no longer purchase anything from Groupon due to boots you advertise for sale," one person wrote on Twitter.

"Poor taste and highly offensive, but I'm glad you felt comfortable selling them.... now I know how you really feel."