A Japanese cosmetic surgeon criticised for praising Nazis and playing down Japan's wartime atrocities won an auction for a memoir by Emperor Hirohito that chronicles the nation's slide into World War Two, paying $275,000 for the document.

Katsuya Takasu, who often appears on TV shows in Japan, has been blasted by a Jewish human rights body, the Simon Wiesenthal Center, for violating "all norms of decency" by dismissing as fabrications the Holocaust and the Nanjing massacre in China.

"I think both Nanjing and Auschwitz are fabrications," Takasu said in a message on social network Twitter in October 2015. "There was no doubt that the Jews were persecuted," he has tweeted, but also praised Nazi scientists' contributions to science, medicine and other fields.

Contacted by Reuters on Thursday, Takasu said he bought the handwritten document, known as the "Emperor's Monologue", because he thought it contained a message to royals and the Japanese people, and should be kept in Japan.

The document record events dating from the 1920s, such as Hirohito's stated resolve not to oppose future cabinet decisions. It caused a sensation when made public in 1990, reigniting a debate over the emperor's responsibility for the war.

The account was dictated to one of Hirohito's aides in 1946, when a defeated Japan was occupied by Allied forces and the emperor faced the possibility of being tried as a war criminal - a step that ultimately was not taken.

In a telephone interview, Takasu said his social media posts had been intentionally misunderstood.

"It (the criticism) is from those who have skilfully picked out some of my tweets and maliciously interpreted them and it is a misunderstanding," he said.

"If you look at all my tweets, I am clearly against Nazism. But I do highly evaluate the wonderful medicine of that era."

But Takasu added that he thought the number of people killed in the Holocaust and the Nanjing massacre had been exaggerated - a stance common among Japanese ultra-nationalists.

China says Japanese troops killed 300,000 people in Nanjing between December 1937 and January 1938, while an Allied tribunal put the death toll at about half that.

"What I wanted to say was that it is said that six million or seven million were killed (in the Holocaust) but was that not several tens of thousands?" Takasu asked.

"It is said that 300,000 were killed in the Nanjing massacre but was that not 6,000 to 7,000 people instead? That is what I meant by 'fabrication.'"

Hirohito's memoir ends with his statement that if he had vetoed the decision to go to war, it would have resulted in a civil conflict that would have been even worse and "Japan would have been destroyed," auction house Bonhams said on its website.

Academics say Hirohito's responsibility for the war has never been fully pursued in Japan, largely due to U.S. occupation authorities' decision to retain the emperor as a symbol of a newly democratic nation.

Asked about Hirohito's responsibility for the war, Takasu said that, in his view, the late emperor was absolved when he said he would give his life for the Japanese people.

"At the point the emperor made that comment, he had no sin," he added.

(Editing by Clarence Fernandez)