Japan scrambled fighter jets to the skies above the disputed Diaoyu Islands after it alleged that a Chinese surveillance plane violated its airspace on Thursday, according to The New York Times:

In an embarrassment for the current administration, Japan’s radar systems failed to detect the Chinese surveillance plane Thursday morning, and Tokyo became aware of its presence only after a Japanese Coast Guard ship spotted it near the islands. By the time fighter jets were dispatched to the area from their base in Naha, on the island of Okinawa, the Chinese plane was nowhere to be seen, a Defense Ministry official said.

With the Japanese jets yet to arrive, the Coast Guard was left on its own to confront the Chinese plane. “Do not intrude into Japanese airspace,” the crew of one of its ships radioed the plane, according to the public broadcaster NHK.

“This is Chinese airspace,” the plane’s crew radioed back, according to NHK.

Tensions between China and Japan over the Diaoyu Islands, known in Japan as the Senkaku Islands, spiked in September when Japan’s central government agreed to purchase three of the islets from their private Japanese owners. A string of anti-Japanese demonstrations ensued across China, even turning violent as angry protesters targeted Japanese-owned businesses and products.

While China and Japan have run patrol ships around the islets over the past few months, Thursday marked the first time aircraft had been used by both sides. A Chinese Foreign Ministry Spokesman called the surveillance flight “completely normal” in a Thursday press conference, reiterating China’s stance that the islets are part of Chinese territory and urging Japan to cease its infringement on the territory. A Japanese government official fired back , according to The South China Morning Post:

“Despite our repeated warnings, Chinese government ships have entered our territorial waters for three days in an row,” Japanese Chief Cabinet Secretary Osama Fujimura told reporters.

“It is extremely regrettable that, on top of that, an intrusion into our airspace has been committed in this way,” he said, adding that Japan had formally protested through diplomatic channels.

Japan’s military scrambled eight F-15 fighter jets, the Defence Ministry said. Japanese officials later said the Chinese aircraft had left the area.

It was the first time a Chinese aircraft had intruded into Japan’s airspace near the disputed islands, Japan Defence Ministry said.

Reuters reports that Japanese academics called the incident a “significant escalation,” but Singapore-based maritime security expert Sam Bateman told Voice of America that Thursday’s incident should be viewed as a continuation of the recent brinksmanship between the two sides:

“I don’t see it as a real escalation. I just see it as a demonstration of sovereignty,” says Bateman. “It’s understandable that both parties are going to engage in a bit of ‘tit-for-tat,’ you know fly close, patrol close to these islands, because that’s the way you demonstrate your sovereignty claim.”

At the Financial Times, Mure Dickie breaks down the political implications of the Diaoyu/Senkaku dispute ahead of Sunday’s general election in Japan:

Shinzo Abe, leader of the opposition Liberal Democratic party and favourite to become prime minister, has stressed the need for a more robust defence of the Senkaku.

Mr Abe has promised increased spending on Japan’s coast guard and defence forces, saying more material resources are essential to block Chinese incursions.

The LDP has also pledged to consider stationing Japanese government officials on the islands, a move that would be considered hugely provocative by Beijing.