Japan's prime minister said Thursday he would express "remorse" over World War II in a closely watched statement this month, but his comments left questions about whether he would repeat previous apologies.

Shinzo Abe is readying his remarks for the 70th anniversary of the end of the war, which are expected to be released ahead of August 15, the date Japan announced its surrender to the Allies.

"I will express remorse over the past war," Abe told reporters, adding he would comment on "our post-war path as a pacifist nation, and how Japan should further contribute to the Asia-Pacific region and the world in the future".

The nationalist leader also said he would follow previous explicit prime ministerial apologies over Japan's past "as a whole".

Abe has repeatedly talked of the need for what he calls a "forward-looking attitude" that concentrates on the positive role Japan has played since surrender and continues to play.

That has set alarm bells ringing in China and Korea, which both suffered from Japan's imperial expansion. They say any attempt to tone down explicit apologies made by previous prime ministers should be discouraged.

Abe's comments Thursday, on the 70th anniversary of the Hiroshima atomic bombing, came as a government-appointed panel submits an advisory report on his statement.

"I will make an appropriate decision about the timing and how the statement will be announced after reading the report," Abe said.

In a landmark address to a joint session of the US Congress in April, Abe expressed his "deep remorse" over Japan's actions towards neighbouring Asian nations during World War II.

But he stopped short of a full apology demanded by Beijing and Seoul, especially over the forced recruitment of so-called "comfort women" to serve Japanese soldiers in military brothels.

A landmark 1995 statement by then premier Tomiichi Murayama stated his feelings of "deep remorse" and "heartfelt apology".

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