German ambassador to Prague Christoph Israng tweeted a picture of a Hitler mask on display in the shop window last Friday, the day after Halloween.

"The Czechs suffered so much under the Nazi regime. Why is such trash being sold in Prague's centre now?" the diplomat wrote in a caption.

"Our department is investigating the case," Jaroslav Ibehej, spokesman for the Czech police's organised crime unit, told AFP but declined to provide further details.

Katerina Pisackova, spokeswoman for Prague's central district, said the city had terminated the rental agreement of the shop in the picturesque Lesser Town.

Its owners claimed in the agreement they would sell clothes and "objects representing the traditional Prague culture and the culture of the Czech Republic."

The UNESCO-listed centre of the Czech capital, which dates back to the Middle Ages, is home to a raft of shops criticised for selling offensive or kitschy souvenirs including fur caps with Soviet Red Army insignia or garishly-painted Russian matryoshka dolls.

"Let's admit that some shops tarnish the reputation of the Prague heritage area," central district mayor Pavel Cizinsky said in a statement obtained by AFP.