Japan issued a strong protest Monday over claims that its fighter jets engaged in “dangerous and unprofessional” behavior when they were scrambled over the weekend in response to Chinese aircraft flying between Miyako Island and Okinawa’s main island.

“I have received a report that the Japanese planes did not conduct any close-range interference against the Chinese military planes … or threaten the safety of the Chinese military planes or their personnel,” Chief Cabinet Secretary Yoshihide Suga said.

Suga also denied that the Air Self-Defense Force fighter jets launched “jamming shells.” Such decoy flares are usually used by pilots to fool incoming missiles.

“That China’s military unilaterally announced something clearly different from the facts is extremely regrettable and harms improving ties between Japan and China,” he said. “We have issued a strong protest to the Chinese side.”

Suga’s harsh words came days after the two Asian powers continued their recent tit-for-tat moves in the airspace above the Western Pacific and East China Sea.

The Defense Ministry in Tokyo said the ASDF scrambled fighter jets Saturday after six Chinese military aircraft flew through the strategically important Miyako Strait, bound for the Pacific. There was no violation of Japanese airspace.

The ministry’s Joint Staff Office said that the six Chinese planes consisted of two Su-30 fighters, two H-6 bombers, one Tu-154 surveillance plane and one Y-8 surveillance plane. The Su-30 fighters crossed the strait and then made a U-turn to head toward the East China Sea while the surveillance planes and bombers headed toward the Bashi Channel, south of Taiwan.

China’s Defense Ministry slammed the ASDF scramble, saying that it had “expressed grave concern” over the Japanese fighter jets, which it claimed harassed and shot the decoy projectiles at Chinese air force planes.

“The Miyako Strait is a universally acknowledged international flight passage,” Chinese Defense Ministry spokesman Yang Yujun said in a statement. “The exercise had been planned within this year’s air force training routine. It does not target any specific country nor objective and it adheres to international law and practices.”

Japan’s Defense Ministry said the ASDF fighters scrambled “in compliance with strict procedures that are based on international law and the law governing the Self-Defense Forces.”

Suga, the government’s top spokesman, said Tokyo will keep a steady eye on the “expanding and increasing” actions of the Chinese military in the area.

In a statement posted on its website, Taiwan’s Defense Ministry also noted the long-range exercises — the first such flights since a Dec. 2 telephone call between Taiwan President Tsai Ing-wen and U.S. President-elect Donald Trump stoked anger in Beijing.

According to retired U.S. Marine Col. Grant Newsham, a senior research fellow at the Japan Forum for Strategic Studies in Tokyo, the exercise highlighted the steady strides China’s military has made in recent years — and its willingness to put these improvements into practice.

“The weekend’s incident is the Chinese military brazenly asserting its ability to operate wherever it wants and effectively daring the Japanese to do something about it,” Newsham said.

Saturday’s flight mirrored a similar one by Chinese fighters and bombers through the area late last month. The ASDF also scrambled fighters in response to that flight.

China has accused Japan of “dangerous and unprofessional” provocations — including radar lock-ons of military aircraft — amid a record spike in scrambles by the ASDF.

Beijing and Tokyo have seen a number of incidents in the air and at sea this year as the dispute over the Japanese-controlled Senkaku Islands in the East China Sea continues to boil. This has prompted concern over prospects of an accidental clash of the two Asian giants near the tiny islets, which are known as the Diaoyu in China.

While talks to establish a maritime and air communications protocol intended to prevent accidental clashes between aircraft and vessels have been ongoing between the two sides, implementation of the mechanism has been stalled since Japan effectively nationalized the Senkakus in 2012.

In the meantime, Beijing’s forays into the Western Pacific and East China Sea are expected to continue.

“The number of Chinese and Russian incursions has increased sharply over the last five to six years and there is no sign that this will change in the future,” said Malcolm Cook, a senior fellow at ISEAS-Yusof Ishak Institute in Singapore.

“China is clearly interested in conducting more operations in the Western Pacific and the Miyako Strait is a major passage from the east coast of China to the Western Pacific,” he added. “Over the same period, Japan has increased its focus on defending its remote islands in the East China Sea.”

China’s People’s Liberation Army Air Force announced in mid-September that it would be organizing “regular” exercises that fly past the so-called first island chain — a strategically important entryway into the Western Pacific that includes Japan’s Ryukyu Islands and Taiwan.

In an editorial in the state-run Global Times newspaper late Sunday, Beijing took Tokyo to task for what it said was hype surrounding the exercises.

“Japan must accept the reality that China is increasing its military activities in the Western Pacific,” the editorial said. “The previous absence of a PLA (People’s Liberation Army) presence beyond the first island chain is not a reason for Tokyo to treat international waters as its own. … Tokyo must not read Beijing’s legal actions as provocation.”

Experts say the extensive chains of Pacific islands that ring in China are seen by some in Beijing as a natural barrier that contains China and its navy. But other Chinese military theorists reportedly view the island chains more as benchmarks or springboards for Chinese military operations.

Now, with the exercises, China is showing off its ability to routinely break through the chains.

“This is just one more step in China’s long-term effort to control inside the first island chain — and beyond,” the Japan Forum’s Newsham said.