President Barack Obama kicked off a tour of Asia on Wednesday with a pointed message to China and the entire region: The United States stands resolutely with Japan in a long dispute over some small islands in the East China Sea.

As Obama landed in Japan, news here was dominated by his comments to a Japanese newspaper that the string of islands subject to a bitter Chinese-Japanese dispute fall within the scope of a U.S.-Japan security treaty.

U.S. policy is clear, the president said in written remarks to The Yomiuri Shimbun, that the tiny, uninhabited 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’s statement affirmed longtime U.S. policy; Defense Secretary Chuck Hagel conveyed a similar message last November in a call with Japanese military officials. But by sending the message at the start of a weeklong trip to Japan, South Korea, Malaysia and the Philippines, the president worked to reinforce a key purpose of his voyage, reassuring allies about U.S. commitment in a region that’s anxious about China.

The Chinese government took offense at Obama’s remarks. Foreign Ministry spokesman Qin Gang said the United States “should respect the facts, in a responsible manner abide by its commitment not to choose sides over a territorial sovereignty issue, be cautious on words and deeds, and earnestly play a constructive role for peace and stability in the region.”

China rattled nerves in the region last November when it expanded its airspace to claim control of the air zone over the contested waters between itself and Japan.

But Chinese state media also reported that numerous countries, including China and the United States, have agreed to a code of conduct in order to reduce conflict and encourage communication over any encounters in the East and South China seas.

Obama isn’t visiting China on this trip, but the country will loom large as the United States looks to assure Japan and other allies that its relationship with China won’t affect its relationship with other Asian countries. China’s assertion of a “great power” relationship with the United States has other countries worried that the two will create a relationship that excludes the others.

“We welcome the continuing rise of a China that is stable, prosperous and peaceful and plays a responsible role in global affairs,” the president told the Japanese newspaper. “Our engagement with China does not and will not come at the expense of Japan or any other ally.”

He also made the case for the Trans-Pacific Partnership, a long-delayed trade deal.

The pact, he said, “will help support jobs and growth in all our countries and give an added boost to America and Japan’s economic revitalization.”

After arriving in Tokyo on Wednesday evening, Obama had a 90-minute dinner with Prime Minister Shinzo Abe at one of the city’s top sushi restaurants, Sukiyabashi Jiro, where the 89-year-old chef is a celebrity and a meal with 20 pieces of sushi costs about $300 per person.

“That’s some good sushi right there,” the president said as he emerged from the basement restaurant along with U.S. Ambassador to Japan Caroline Kennedy and National Security Adviser Susan Rice.

While Obama has visited Japan before, this is the first “state” visit by a U.S. president since Bill Clinton. Obama will be greeted Thursday by the emperor, and feted at a state dinner.