SHANGHAI – Japan on Saturday lashed out at UNESCO’s decision to inscribe China’s “Documents of Nanjing Massacre” in its Memory of the World register, calling it “extremely regrettable” and calling for the process to be reformed.

On Friday the U.N.’s cultural and scientific body agreed to 47 new inscriptions, including a request by Beijing to mark documents recording the weekslong mass murder and rape committed by Japanese troops after the fall of Nanking in 1937. The city is presently known as Nanjing.

The massacre, often referred to as the Rape of Nanking, is an exceptionally sensitive issue in the often-tense relations between Japan and China, with Beijing charging that Tokyo has failed to atone for the atrocity.

Japan had called for the documents not to be included and accused UNESCO Saturday of being politicized.

“It is extremely regrettable that a global organization that should be neutral and fair entered the documents in the Memory of the World register, despite the repeated pleas made by the Japanese government,” the Foreign Ministry said in a statement.

“As a responsible member of UNESCO, the Japanese government will seek a reform of this important project, so that it will not be used politically,” the statement added.

The UNESCO decision came after a two-year process during a meeting of experts tasked with studying nominations from 40 countries.

The new inscriptions were agreed to at a meeting that ran from Sunday to Tuesday and was held in the United Arab Emirates.

Beijing’s dossier on the widespread orgy of killings of Chinese citizens and soldiers following the 1937 capture of Nanking by the Japanese military is among dozens of new additions of documentary heritage, including two sets of archives from Japan.

The Japanese materials cover the postwar internment and repatriation of Japanese by the Soviet Union and a Buddhist temple’s extensive records of its activities from the medieval to pre-modern eras in Japan.

China had also nominated “comfort women” files about the “sex slaves for Imperial Japanese troops.” But this was not added in the biennial registration by UNESCO for the documentary version of the World Heritage and Intangible Cultural Heritage programs, which started in 1997.

The “Documents of Nanjing Massacre” submission consists of court documents from the International Military Tribunal for the Far East that convicted several Japanese as war criminals and a Chinese military tribunal, among others. They also include photos of the killings said to have been taken by the Imperial Japanese Army and film footage taken by an American missionary.

Differences over history have complicated Japan’s relations with China. Japanese officials may be concerned that UNESCO’s registration of the massacre documents could give Beijing ammunition against Tokyo in promoting its campaign to highlight what it calls “the crimes of Japanese militarism,” including the massacre, in which it claims more than 300,000 people were killed.

The Imperial Japanese military invaded China in the 1930s and the two countries fought a full-scale war from 1937 until Japan lost World War II in 1945.

China says 300,000 people died in a six-week spree of killing, rape and destruction after the Imperial Japanese Army entered Nanking.

Some respected foreign academics put the number lower but there is very little mainstream scholarship doubting that a massacre took place.

China historian Jonathan Spence, for example, estimates that 42,000 soldiers and citizens were killed and 20,000 women raped, many of whom later died.

In Japan, however, some question that view entirely, particularly among some conservatives and nationalists.

In February, a senior executive at public broadcaster NHK denied the massacre, reportedly dismissing accounts of it as “propaganda.”

Japan’s official position is that “the killing of a large number of noncombatants, looting and other acts occurred,” but it adds “it is difficult to determine” the true number of victims.

In April this year, Japan rebuffed protests about newly approved textbooks after complaints that they failed to use the word “massacre” when referring to the mass slaughter in Nanking, opting for the term “incident.”

Tokyo frequently clashes with many of its Asian neighbors over its war record, with many accusing Tokyo of failing to atone for its atrocities or recognize the suffering that took place under the yoke of Japanese militarism.

Last year China nominated the “Nanjing Massacre” files and the comfort women documents for UNESCO listing this year on the 70th anniversary of what Beijing calls its victory in the war of resistance against Japanese aggression and in the world war against fascism.

Tokyo argued that China was politicizing UNESCO and asked Beijing to withdraw the double nominations, which China refused to do, according to Japanese officials.

Japanese historian Masato Miyachi, a professor emeritus of the University of Tokyo, said, “By registering the (Nanjing) materials as Memory of the World heritage, UNESCO is recognizing the authenticity of documents and their significance in the world.”

He noted that there are other UNESCO-listed documents about dark episodes in history, such as war and slavery. “If, however, the veracity of the documents submitted by China is questioned, that would undermine the credibility of the entire Memory of the World heritage,” he said.

According to the Japanese Foreign Ministry, the Memory of the World screening criteria concern the necessity of the preservation and custody of documents, and whether they represent historical truth is not considered.

The Memory of the World register, set up in 1992, is aimed at preserving humanity’s documentary heritage, and currently holds 348 documents and archives that come from countries all over the world.

“It is my deep and firm conviction that the Memory of the World Programme should be guided in its work to preserve documentary heritage and memory for the benefit of present and future generations in the spirit of international cooperation and mutual understanding, building peace in the minds of women and men,” UNESCO director Irina Bokova said.

One of the two sets of documents listed from Japan is a collection of some 570 memoirs, drawings and other items composed by Japanese inmates imprisoned in Siberian labor camps after the war, and lists of those repatriated afterward to Maizuru port in Kyoto.

Roughly 55,000 of the nearly 600,000 Japanese soldiers detained in labor camps in Siberia and Mongolia after the war died from forced labor, severe living conditions and malnutrition.

Before applying for registration, the Maizuru city government investigated other documents with the help of its sister city Nakhodka, near Vladivostok, in eastern Russia. Japan and Maizuru applied to register those documents in March 2014.

The other collection is the archives at Toji Temple called the Toji Hyakugo Monjo (Toji Temple’s 100 boxes of documents), comprising some 25,000 documents from the years 763 to 1711. The collection — records of the ancient temple system and social structures — was designated a National Treasure in 1997.

In the next registration phase in 2017, Japan will seek to list the records of diplomat Chiune Sugihara, who issued visas to help some 6,000 Jews flee Nazi persecution during WWII, as well as three ancient stone monuments and documents of Korean missions to Japan during the Edo Period.