Takaichi suggested last month that Japan would intervene militarily in any Chinese attack on the self-ruled island that Beijing claims as its own and which it has not ruled out seizing by force.
J-15 jets from China's Liaoning aircraft carrier on Saturday twice locked radar on Japanese aircraft in international waters near Okinawa, according to Japan.
No damage or injury was caused, but it was the first time that Japan had disclosed such an incident.
Fighter jets use their radar for fire control to identify targets as well as for search and rescue operations.
Japan had scrambled its F-15 jets because it was worried about possible "airspace violations", chief government spokesman Minoru Kihara said Monday.
China's navy said Sunday that the Japanese planes "repeatedly approached the Chinese Navy's training area and caused trouble, seriously affecting the normal training of the Chinese side and seriously endangering flight safety."
A statement said that Tokyo's claim was "completely inconsistent with the facts" and told Japan to "immediately stop slandering and smearing".
Kihara responded on Monday that China's "claim that the Self-Defense Forces aircraft seriously obstructed the safe flight of Chinese aircraft is unfounded."
Vice Foreign Minister Takehiro Funakoshi summoned ambassador Wu Jianghao on Sunday and "made a strong protest that such dangerous acts are extremely regrettable".
Funakoshi "strongly urged the Government of China to ensure that similar actions do not recur," the Japanese foreign ministry said late Sunday.
Takaichi said the same day that Japan would "respond calmly and resolutely."
Beijing's foreign ministry said it rejected that protest, and had lodged its own counter-protest, according to state news agency Xinhua.
- Rare earths -
The comments on November 7 about Taiwan by Takaichi, seen before she became premier in October as a China hawk, have enraged Beijing.
China has urged its citizens to avoid Japan -- they are the biggest source of tourists -- and cultural events involving Japanese performers and movies have been hit.
Last week Japanese and Chinese vessels engaged in a fresh standoff around disputed islands administered by Japan in the East China Sea that have long been a flashpoint.
Aside from reportedly renewing a ban on Japanese seafood imports, China has however so far stopped short of imposing more serious economic measures such as curbing exports of rare earth metals.
But the Yomiuri Shimbun daily reported on Sunday that China's export permit procedures for rare earths -- key ingredients for smartphones and electric vehicles -- to Japanese companies were taking longer than usual.
Kihara told reporters that there have been "no significant changes", adding however that China's existing control measures were having a "serious impact on the global supply chain."
Tokyo says Chinese jets locked radar onto Japan fighters
Tokyo (AFP) Dec 7, 2025 -
Chinese military aircraft locked radar onto Japanese fighter jets southeast of Okinawa's main island, Japan's defence ministry said on Sunday.
China's navy said Tokyo's claim was "completely inconsistent with the facts" and told Japan to "immediately stop slandering and smearing".
Relations between Tokyo and Beijing have soured following remarks by new Japanese Prime Minister Sanae Takaichi suggesting that Tokyo could intervene militarily in any attack on Taiwan.
Chinese J-15 fighter jets twice locked radar on Japanese fighter jets on Saturday, without causing damage or injuries, Japan's defence ministry said.
Fighter jets use their radar for fire control to identify targets as well as for search and rescue operations.
Defence Minister Shinjiro Koizumi said the incident was "dangerous and extremely regrettable", adding that Japan had lodged "a strong protest" with China.
Beijing's foreign ministry said it rejected that protest, and had lodged its own counter-protest, according to state news agency Xinhua.
A foreign ministry spokesperson, cited by Xinhua, urged Japan to "immediately stop its dangerous moves of harassing China's normal military exercise and training".
- 'Deeply concerned' -
The two countries have a long-running territorial dispute over the Senkaku Islands, known as the Diaoyu in China.
The tiny, uninhabited islands lie between Okinawa and Taiwan, the much larger self-ruled island that China also claims.
Beijing summoned Tokyo's ambassador following Takaichi's comments last month.
Tokyo is deepening cooperation with US allies in the Asia-Pacific region, where several countries have territorial disputes with China.
Beijing, for instance, claims nearly all of the South China Sea, and has been asserting control more strongly in parts of the strategic waterway despite an international ruling that its claim has no legal basis.
The incident at the weekend came as Australia's Defence Minister Richard Marles was visiting Japan.
Marles said he was "deeply concerned by the actions of China in the last 24 hours", following a meeting with his Japanese counterpart.
He said Canberra had "stabilised" its relationship with China by "acting in a clear, consistent, calm and sensible way".
"We will seek to work together with China where we can, but we will disagree where we must," he said in response to a question about supply chains.
Marles also visited Mitsubishi's shipyard in Nagasaki, months after Canberra signed a major $6 billion deal to buy 11 advanced warships from the Japanese firm.
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