The German ambassador to the Czech Republic posted a picture of the shop stock to Twitter, asking why "such trash" was being sold in central Prague.
Police in the Czech Republic have launched an investigation into complaints that a mask depicting Adolf Hitler was spotted on sale in a shop in Prague.
Christoph Israng, the German ambassador to the Czech Republic, tweeted a picture of the mask the day after Halloween as he passed the shop.
"The Czechs suffered so much under the Nazis," he wrote, adding: "Why is such trash sold in the middle of Prague?"
Among the dozens of responses, Czech Interior Minister Jan Hamacek said police had since begun an investigation into the shop.
The Czech police also confirmed to Euronews that it was "dealing with this matter", but said it was "not at liberty to provide more information at this time."
Meanwhile, a spokeswoman for Prague's central district told AFP the shop had since lost its rental agreement in the Malá Strana district.
"Let's admit that some shops tarnish the reputation of the Prague heritage area," the mayor of the city's central disctrict, Pavel Čižinský, was quoted by AFP as saying.
Hundreds of thousands of people were killed — many of them Jews — under the Nazi occupation between 1938 and 1945 of what was fomerly known as Czechoslovakia.