It was the latest development in the fractious relations between the tiny Alpine principality and its much larger neighbor to the north.
In a letter sent by Liechtenstein's Hans-Adam II to the Jewish Museum in Berlin, the prince declared that his nation "has already outlasted three German empires in the past 200 years.
"I hope we will also outlast a fourth," he added in the letter, which was reprinted in Thursday's edition of Swiss newspaper Tages-Anzeiger.
Germany was known as the Third "Reich" meaning 'third empire' between 1933 and 1945 when Adolf Hitler's National Socialist Party was in power and systematically persecuted Europe's Jews.
"Describing the Federal Republic of Germany as a Fourth Reich places it in one line with the Third Reich, and trivializes the crimes of the Nazis in an irresponsible manner," museum spokeswoman Eva Soederman told The Associated Press.
The prince could not immediately be reached for comment. But a statement from his office said Hans-Adam "in no way intended to play down the horrific events of the Third Reich. Rather, the letter refers to the clearly difficult issue of dispossession during the Second World War and afterwards."
The museum received the letter in June. In it, Hans-Adam told Jewish Museum director Michael Blumenthal he would not loan the museum a painting by 17th century Dutch artist Frans Hals because Germany had shown itself to be "less and less inclined to abide by basic principles of international law."
The prince has waged numerous legal battles in Germany to recover artwork he claims was looted from his family by the Nazis during the Second World War.
Soederman said the painting "Portrait of a Man" was supposed to be part of an exhibition later this month about looted art.
A senior member of Germany's Central Council of Jews said he expects Hans-Adam to apologize to Blumenthal, a former U.S. treasury secretary whose family fled Nazi Germany in 1939.
"The prince's comments are completely absurd," the vice-president of Germany's Central Council of Jews, Salomon Korn, told Tages-Anzeiger.