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."