TOKYO -- U.S. forces staged a rare military exercise near the Japan-administered Senkaku Islands, going a step beyond its usual activity by airdropping supplies into waters near the islets in an apparent warning to China over recent incursions.
The U.S. military informed Japan's Self-Defense Forces shortly beforehand about plans for an exercise there involving a personnel drop, according to a senior Japanese official, though no troops were ultimately transported onto the islands.
The drill took place in February, a few weeks before a summit of the Indo-Pacific security grouping known as the Quad.
The tensions surrounding the Senkakus, which China claims as the Diaoyu, have taken on added significance as Beijing has ramped up pressure on Taiwan. The islands sit only about 170 km away from the Taiwan Strait, and mounting tensions with China in either area could easily come to engulf both.
A Chinese fighter jet approached the islands on the day of the drill, and Japanese Air Self-Defense Force fighters were scrambled in response. Chinese naval vessels were also sighted in the vicinity.
Japanese Chief Cabinet Secretary Katsunobu Kato declined Thursday to comment on the specifics of a U.S. operation, but said that "American forces conduct drills from time to time during peacetime as needed to fulfill the objectives of the Japan-U.S. Security Treaty."
Washington and Tokyo have affirmed repeatedly -- most recently in the joint statement issued after the April 16 summit between U.S. President Joe Biden and Japanese Prime Minister Yoshihide Suga -- that Article 5 of the treaty, which obligates the U.S. to defend Japan if it comes under attack, covers the Senkakus.
The language of the treaty suggests that if Chinese troops landed on the islands, for example, American forces would work with the SDF to retake them or stop the invasion.
While the U.S. military and the SDF have previously conducted exercises around isolated islands for such scenarios, this appears to be the first to come to light involving the Senkakus themselves.
"It was a warning to China against escalating activity in the area after enacting the coast guard legislation," said Yoshihiko Yamada, a professor at Tokai University. That law, which took effect in February, authorizes China's quasi-military coast guard to fire on foreign ships under certain circumstances.
The move reflects a shift in Washington's attitude toward Beijing. Biden has called China America's biggest rival, and his administration has made clear that it seeks to partner with allies to counter Beijing on both security and economic fronts.
The decision to take action specifically related to defending the Senkakus, a major concern for Tokyo, is part of this change. The topic was raised at last week's summit, after which Suga told reporters that he and Biden agreed to "peacefully resolve" issues involving China.
Beijing has acted increasingly aggressively in the area. The number of days on which Chinese vessels sailed in the territorial waters around the Senkakus between January and March doubled from the same period last year, and Chinese ships have passed through the islands' contiguous zone every day since Feb. 13.
For Tokyo, having the U.S. military step up activity around the Senkakus should serve as a powerful deterrent. But it also means that escalating friction between Washington and Beijing could spur more Chinese incursions around the islands. And American drills in the area create the risk of an accidental clash.
That would force Japan to take responsibility for its own defense under even more difficult circumstances than those it faces now. As Washington steps up its role, Tokyo will need to will bolster its own capabilities.
It could also face pressure to cooperate with American forces in the event of a Taiwan Strait conflict, as the mention of the strait in last week's joint statement suggests.
Some in the Japanese government and the ruling Liberal Democratic Party advocate stepping up joint Japan-U.S. drills in case of a conflict around the Senkakus. The idea of legislation allowing SDF involvement in less serious situations has been floated as well.