A Japanese newspaper apologized Saturday for running an advertisement promoting books about “a conspiracy by the Jewish-controlled U.S.”

Sankei Shimbun published an apology--a rare climb-down for the conservative newspaper—saying it received a letter of protest from the Simon Wiesenthal Center, a Los Angeles-based human rights group.

"It is extremely regrettable that such disreputable content was published and was delivered to our readers," Takamitsu Kumasaka, president of the Sankei Shimbun. "I deeply apologize to our readers and to every member of the Jewish community."

At a time when Japan's Prime Minister Shinzo Abe has been pushing for patriotism at school and more nationalistic interpretations of the nation's history, there are fears about an increase in hate speech toward ethnic minorities in Japan. A man was arrested this year for ripping pages out of books, in public libraries and a bookstore in the Tokyo area, on Holocaust victim Anne Frank.

The books that are the subject of the advertisements are authored by Richard Koshimizu, a self-claimed freelance journalist. In one book, he argues that the 2011 Tohoku earthquake was set off by a U.S. military bomb, while another says the Holocaust was a myth spread by the Soviet Union. A third book claims the election of Mr. Abe's government in 2012 was part of a Jewish plan for global domination.

"The Sankei Shimbun considers the Holocaust by Nazi Germany as an unforgivable and hateful crime," Mr. Kumasaka said. The newspaper doesn't support the thinking of those who subscribe to Jewish conspiracy theory, he added.

Mr. Koshimizu and the Simon Wiesenthal Center were not immediately available for comment.

The Sankei isn't new to controversy. Its former Seoul bureau chief was indicted in South Korea in October for publishing a story that South Korea considered as defamatory to President Park Geun-hye--an allegation the newspaper fiercely denies.

The Sankei also attacks liberal newspapers such as Asahi Shimbun, which recently retracted articles about Korean "comfort women" -- prostitutes forced to serve Japanese soldiers at brothels during World War II -- after being unable to verify some of the witness accounts.

The Yomiuri Shimbun also apologized last month for using the words "sex slaves" to describe "comfort women" in the past articles.