Last week US President Barack Obama visited Tokyo and Seoul, the first two legs of his ongoing tour of Asia, which is intended to reaffirm Washington’s commitment to the region. His itinerary also includes Malaysia and the Philippines.

In Tokyo, Obama gave a big boost to Japanese Prime Minister Shinzo Abe by unequivocally pledging to protect the Senkaku islands against China.

At a joint news conference after the summit, Obama said, “Let me reiterate that our treaty commitment to Japan’s security is absolute, and Article 5 covers all territories under Japan’s administration, including the Senkaku Islands.”

Article 5 of the US-Japan Treaty of Mutual Cooperation and Security obliges the US to defend Japan should a third country attack “the territories under the administration of Japan.”

Obama’s security pledge was significant as it was the first time that a US president explicitly stated that the bilateral security treaty would apply to the disputed islands. An adviser to Abe described it as “the most reassuring statement that the nation has ever heard” from Washington.

Abe was also delighted with Obama’s reassurances. So much so that he described the joint statement released one day after the summit as “groundbreaking” for the two countries.

Obama was at first opposed to specifically mentioning Senkaku as it would antagonise China. Beijing also lays sovereignty claims to the islands, which it calls Diaoyu.

He reportedly changed his mind following Russia’s forceful annexation of Crimea. Tokyo officials asserted that if Obama stopped short of referring to the disputed islands, it could send the wrong signals to China.

But quite expectedly, China lashed out at Obama’s security pledge and denounced the US-Japan alliance as a legacy from the Cold War. The spokesman of the Chinese Foreign Ministry said the alliance should not harm China’s territorial rights.

Yet China is unlikely to take Obama’s statement seriously. Beijing officials are well aware that it does not signal a shift in Washington’s policy as US officials, including State Secretary John Kerry, have reiterated the stance.