Online marketplace Etsy has apologised after a T-shirt emblazoned with the words Camp Auschwitz was found for sale on its site.
The Auschwitz Memorial called the T-shirt "painful" and "disrespectful" to victims of the death camp and asked for the item to be taken down.
Etsy said it had immediately banned the seller on becoming aware of the item.
But it faced fury online as it emerged one of the rioters who stormed Congress had worn a Camp Auschwitz top.
More than a million people were murdered at the Auschwitz concentration camp in Poland by the Nazis during World War Two, most of them Jews.
The T-shirt, which also featured a skull and crossbones, was posted on Etsy by a US seller and available to buy in the UK for £19.95.
According to to reports, the listing described the T-shirt as "everything you've dreamed of and more" and "flattering for both men and women".
The Auschwitz Memorial thanked Etsy for swiftly taking down the listing, but many still reacted angrily on Twitter.
One person on Twitter replied to The Auschwitz Memorial: "It is insane that you have to make this request. Shame on Etsy to allow such a horrendous thing to be offered in your shop - who allowed this? This is unacceptable!"
Some people called for a boycott of Etsy but others urged against this, saying it would only hurt independent sellers who used the platform legitimately.
"Etsy is like an EBay for handcraft sellers... there are one or two bad apples like this but hundreds of great hand crafters who rely on Etsy for their income," one tweeted.
"Instead of boycotting you can report this listing at the bottom of the page."
On 6 January rioters breached the US Capitol in Washington in a bid to block certification of the US presidential election result. Five people died including a policeman.
The mob - which included members of far-right groups such as the Proud Boys - had been encouraged by President Trump as part of his attempt to overturn his election defeat.
An Etsy spokeswoman said: "We are deeply saddened by the events that took place at the US Capitol.
"Etsy's long-standing policies prohibit items that promote hate or violence, and we are vigilantly monitoring our marketplace for any such listings that may have been inspired by recent unrest.
It said: "We removed this item immediately when it was brought to our attention and have also banned the shop that attempted to list this item. Items that glorify hate or violence have no place on Etsy and we are committed to keeping our marketplace safe."