Police are investigating the sale of Adolf Hitler masks at a shop in the capital of the Czech Republic, local media report.
German ambassador Christoph Israng pictured the mask on display in a souvenir shop in Prague.
"The Czechs suffered so much under the Nazi regime," Israng tweeted. He did not name the shop.
An investigation has been launched to determine whether any laws have been broken, police said.
"I can confirm that we are dealing with the case of mask sales in the centre of Prague," a police spokeswoman told Czech news agency CTK.
In reply to Israng's tweet, Czech's interior minister Jan Hamacek said police were dealing with the matter.
Israeli ambassador Daniel Meron also weighed in on Twitter, condemning the masks as an "affront to Holocaust survivors".
The sale of Hitler masks at the same shop was brought to light by a Jew reporter earlier this year.