TOKYO (AFP) - Japan's top government spokesman on Wednesday declared himself dumbfounded after a recent prime minister said he understood China's claim to islands at the centre of a bitter row between Tokyo and Beijing.

Yukio Hatoyama, whose brief term as premier was almost universally regarded as a flop, told Hong Kong-based Phoenix Television it was "unavoidable" that China believed Japan "stole" the Senkaku islands.

The uninhabited outcrop in the East China Sea, which Beijing claims as the Diaoyus, is the subject of a decades-old dispute that has flared badly in the last year. Both countries continue to send official ships to the area to press their ownership.

Japan says it brought previously unclaimed islands under its control in 1895. China says they were illegally snatched and should have been returned alongside other occupied territories after World War II.

During the interview, which was broadcast in China on Tuesday, Hatoyama said: "It is unavoidable that the Chinese side thinks Japan stole" the islands.

As a media storm gathered, he told Japanese reporters later in the day that he had meant to say there was "a possibility" that China might think that way.

Japan's Chief government spokesman, Yoshihide Suga, said Hatoyama's comments were "outrageous".

"I was completely at a loss for words when I heard about his remarks. It was literally jaw-dropping," he told a news conference Tuesday.

"It is outrageous and unforgivable that a former prime minister before has said things that hurt our national interests," Suga said.

Asked again on Wednesday about the episode, Suga said he had still not recovered his tongue.

"I said yesterday that I was left open-mouthed. I still remain so, my mouth remains open," he said.

Despite the regular stand-off between official vessels at the islands, Japan's stated position is that there is no dispute over the archipelago.

Hatoyama, who led the now-opposition Democratic Party of Japan and served as prime minister between September 2009 and June 2010, has left politics, but as heir to the Bridgestone tyre empire remains active in business circles.

His time in office was marked by confusion and policy flip-flops, including on the US military presence in Okinawa, which managed to alienate voters and irritate Washington without achieving any drawdown of troops.

He is no stranger to controversy and is seen as something of a liability even among Japanese politicians, a class of people who have a tendency to put their feet in their mouths.

Earlier this year, his visit to the Nanjing Massacre Memorial, which marks the scene of one of the Japanese Imperial force's worst wartime atrocities, caused consternation at home when he said he felt "responsibility" for the outrage.

Nicknamed "The Alien", in part because of his wide-eyed expression, Hatoyama's sometimes oddball comments proved a stumbling block for party managers.

He is a fourth-generation politician and the second in the family to become prime minister, after his grandfather. His other grandfather founded Bridgestone.

Hatoyama's wife Miyuki is a former actress who became a lifestyle guru with an interest in spirituality. She famously said her soul once visited Venus on a triangular spaceship and that she met Tom Cruise in a previous life.