The islands at the centre of a row between Tokyo and Beijing are covered by the US-Japan defence alliance, Barack Obama told a newspaper ahead of his arrival in Tokyo.

Obama, who begins a tour of Asia that will also take in South Korea, the Philippines and Malaysia, is the first sitting US president to explicitly affirm that hostile action against the island chain would spark an American reaction.

'The policy of the United States is clear - the Senkaku Islands are administered by Japan and therefore fall within the scope of Article 5 of the US-Japan Treaty of Mutual Cooperation and Security,' Obama said in a written interview with the Yomiuri Shimbun.

'And we oppose any unilateral attempts to undermine Japan's administration of these islands,' he said.

Several senior US figures, including former secretary of state Hillary Clinton and Secretary of Defense Chuck Hagel have made similar statements, which Tokyo covets as a way to warn China away from territories it claims as the Diaoyus.

Obama's week-long tour of Asia is being dubbed a 'rebalancing' eastward of US foreign policy by the White House.

Although China is not on his itinerary, its presence will be felt on every leg at a time of complex regional disputes and questions about US strategy.

The row over ownership of the Senkakus is not new, but has burst to the fore in the past two years, with paramilitary vessels from both sides jostling in nearby waters to assert control.

In November, China declared an air defence identification zone over the East China Sea, including the skies above the islands.

'I've also told (Chinese) President Xi (Jinping) that all our nations have an interest in dealing constructively with maritime issues, including in the East China Sea,' Obama told the Yomiuri.

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Disputed islands part of alliance