The architect of a landmark Japanese apology for World War II crimes on Monday urged Prime Minister Shinzo Abe to follow his lead on the 70th anniversary of the end of hostilities.

Former premier Tomichi Murayama, whose 1995 statement is widely seen as the high watermark of Japanese contrition for historic wrongdoing, said the words of the country's leader carried real gravitas.

"If it had just been my personal statement, it would have had little value, but it was adopted by the cabinet and so its weight is different," Murayama said in Tokyo Monday.

"Successive cabinets have since promised the world they would follow the statement," he said, referring to the document's expression of "deep remorse" and its "heartfelt apology".

The so-called Murayama Statement noted that Japan "through its colonial rule and aggression, caused tremendous damage and suffering to the people of many countries, particularly to those of Asian nations".

But the 91-year-old Murayama said Abe appears ready to "dilute" the apology when he makes his own statement later this year.

"I think that's wrong," he added.

Abe's language is being closely watched by China and South Korea, who suspect him of being a historical revisionist bent on re-forging global opinion of Japan's warring.

Beijing and Seoul vociferously argue that Tokyo has not properly atoned for its actions in the 1930s and 1940s, and does not fully accept its guilt, insisting that the Murayama Statement is the standard against which future utterances be judged.

Last month, Abe said he may not issue a direct apology for Japan's past aggression, saying as long as he says he agrees with what was written in the previous statements, "I don't think I need to write it again".

Abe wants Japan to have what he says is a less masochistic view of its history. He has caused waves by quibbling over the definition of "invade" and provoked anger by downplaying Tokyo's formalised system of sex slavery in military brothels.

In the speech Monday, Murayama criticised Abe for his campaign to revise the country's pacifist constitution as "really dangerous."

Abe, a third-generation politician whose grandfather was a World War II cabinet member and became a post-war prime minister, has long agitated for revision.

US occupying forces imposed the constitution in the aftermath of World War II, but its war-renouncing Article Nine is held dear by many Japanese.