Japanese Prime Minister Shinzo Abe has infuriated his country's neighbours by seeming to question whether his country really invaded China and Korea during the Second World War.

The remarks, which were made in Japan's parliament, come at a time when East Asia is already on edge. North Korea has been threatening nuclear war against the United States and South Korea for more than a month, while regional giants China and Japan have this week resumed butting heads over a disputed chain of islands.

Now Mr. Abe is picking at the wounds left by his country's brutal invasion and occupation of the Korean Peninsula and much of China during the Second World War.

Story continues below advertisement

"The definition of what constitutes aggression has yet to be established in academia or in the international community," Mr. Abe said on Tuesday, according to Japan's Asahi Shimbun newspaper. "Things that happened between nations will look differently depending on which side you view them from."

In some translations, the hawkish Mr. Abe was quoted wondering about "what constitutes invasion." Japanese language experts said "invasion" and "aggression" were both valid translations of what Mr. Abe said.

Mr. Abe, whose right-wing Liberal Democratic Party won a landslide election in December, also questioned his country's pacifist post-war constitution, saying it had been drafted by "occupying forces." Japan was under U.S. administration in 1947 when two American military officers drafted the constitution, which prohibits acts of war and limits the scope of the Japanese military.

"It's like saying Hitler's invasion of Poland wasn't really an invasion. If a German chancellor had said the same thing, he or she would have had to resign," South Korean political scientist Ko Sang-tu told the Chosun Ilbo newspaper.

An estimated 20 million people were killed in China between the outbreak of war in 1937 and Japan's surrender to Allied forces in 1945. In Korea, which was first annexed by Japan in 1910, hundreds of thousands of men were used by Japanese troops as slave labourers during the Second World War, while hundreds of thousands of women were forced to become "comfort women" for the Japanese army.

Mr. Abe made his remarks in response to a question in parliament about his government's position toward a 1995 apology issued by Japan's then-prime minister, Tomiichi Murayama, for Japan's "colonial rule and aggression" in Korea.

Mr. Abe isn't alone in his revisionism. He spoke the same day that a record 168 Japanese lawmakers visited the controversial Yasukuni Shrine – where 14 Class A war criminals are among the honoured soldiers – drawing howls of protest from Beijing and Seoul, where visits to Yasukuni are seen as symbolic of Japan's refusal to atone for its crimes against its neighbours. Former prime minister Taro Aso, now Mr. Abe's Deputy Prime Minister, visited, while Mr. Abe – who visited last year while opposition leader – sent a ritual offering.

Story continues below advertisement

"The controversial visits once again prove that Japan is the troublemaker and provocateur in East Asia," read an editorial Wednesday in the Global Times, a nationalist newspaper affiliated with China's ruling Communist Party. "Japan has once again been the one that broke the uneasy regional balance."

The remarks add fuel to an already flammable confrontation with China over the ownership of five uninhabited islands in the East China Sea, one that has seen China repeatedly send ships into Japanese-controlled waters to back its territorial claim.

On Tuesday, after eight Chinese ships entered the waters around the islands – which are known as Senkaku in Japan and Diaoyu in China – Mr. Abe warned that any attempted Chinese landing would be repelled "by force."