The islands at the center of a corrosive row between Tokyo and Beijing are covered by the U.S.-Japan defense alliance, Barack Obama told a newspaper ahead of his arrival in Tokyo Wednesday.
Obama, who begins a tour of Asia that will also take in South Korea, the Philippines and Malaysia, is the first sitting U.S. 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 U.S.-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 U.S. 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 "re-balancing" eastward of U.S. 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 U.S. strategy.
The row over ownership of the Senkakus is not new, but has burst to the fore in the last two years, with paramilitary vessels from both sides jostling in nearby waters to assert control.
In November, China declared an air defense 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.
"Disputes need to be resolved through dialogue and diplomacy, not intimidation and coercion," he said.
As well as a degree of hand-holding with Asian allies who feel a little neglected, Obama will be striving to show Beijing that the U.S. poses no threat and does not intend to contain it.
"We welcome the continuing rise of a China that is stable, prosperous and peaceful and plays a responsible role in global affairs. And our engagement with China does not and will not come at the expense of Japan or any other ally," Obama said.
Obama also said Washington has "enthusiastically welcomed Japan's desire to play a greater role in upholding international security" in areas of disaster relief and UN peacekeeping operations.
"I commend Prime Minister (Shinzo) Abe for his efforts... to deepen the coordination between our militaries, including by reviewing existing limits on the exercise of collective self-defense" which allow Tokyo to protect its ally Washington in Asian security, Obama said.
Obama and Abe are due to have an informal dinner late Wednesday, with local media speculating it will be at a tiny sushi bar that has three Michelin stars but only a handful of seats and featured in the documentary "Jiro Dreams of Sushi".