TOKYO (AFP) - Emperor Hirohito, the demi-god at the apex of the Japanese state when it waged bloody war across Asia, cautioned against conflict but celebrated military success, according to the long-awaited official history of his reign, released Tuesday.

The mammoth 61-volume set, which has taken 24 years to compile at a cost to the Japanese taxpayer of 230 million yen (S$2.7 million) reveals little new hard evidence about one of the most controversial figures of the 20th century.

But it offers a largely sympathetic view of the man considered by some to have played a pivotal role in Japan's march to World War II, and by others as the helpless puppet of an out-of-control military state.

The annals, produced by the Imperial Household Agency, show how in the lead-up to Japan's surprise attack on the United States fleet at Pearl Harbour in December 1941, Emperor Hirohito warned against a "reckless war" that would make him feel "deeply sorry for my imperial ancestors". They depict a man who spoke out against the military commanders who had taken Japan into full-scale war against China in 1937 with the promise that the conflict would be short and that victory was assured.

But they also show a leader satisfied with triumphs on faraway battlefields.

An increasingly militaristic Japan had invaded Manchuria in 1931, where it established a puppet government and a base from which to agitate against China's weak regime.

In 1937, imperial troops took the then-Chinese capital of Nanjing in an orgy of violence, where tens of thousands of civilians were butchered.

After being briefed about the fall of the city, Emperor Hirohito told military leaders to tell their officers and soldiers: "I am deeply satisfied by their courage in quickly bringing down the capital Nanjing."

Documents used in compiling the Hirohito record include information about how Japanese troops surrounded and attacked the city, but did not contain details of the massacre of civilians, Kyodo News reported.

The episode continues to poison Sino-Japanese relations, not least because a minority on Japan's right insist it was a legitimate military operation, denying contemporaneous evidence of the slaughter of non-combatants.

Emperor Hirohito is a particularly divisive figure among historians because of his unique position.

Some hold that as a living god, who was simultaneously commander in chief of Japan's military, he had the final say over the wars that the country waged in the 1930s and 1940s.

They insist the invasion and occupation of China, which Chinese sources claim cost up to 20 million lives, would not have happened without at least tacit approval from him.

When Japan surrendered in 1945, the US-led occupying force kept Emperor Hirohito on the throne, mindful of the need for stability, even as they arrested, tried and hanged numerous military and political leaders.

In exchange for being allowed to live unmolested, Emperor Hirohito had to renounce his divinity.

He continued to act as symbol of the nation until his death in 1989, overseeing the country's transformation from militarism to democracy and market capitalism, along with the enormous wealth that brought.

He remained controversial around the world, and was the target of protests during foreign tours, including to Britain in 1971, where former Japanese prisoners of war turned their backs on him as he was driven through London.

His disputed legacy is understood to have been a factor in the length of time it has taken for the Imperial Household Agency to produce the annals.

The agency said it used 3,152 documents, including 40 new items, to compile the 12,000-page record.