J-15 fighters from China's Liaoning aircraft carrier, South China Sea, January 2, 2017. REUTERS/Mo Xiaoliang. FILE PHOTO

By Tim Kelly, Kiyoshi Takenaka and David Kirton

TOKYO, Dec 7 (Reuters) - Japan said on Sunday that Chinese fighter jets had aimed their radar at Japanese military aircraft in two "dangerous" incidents near Japan's Okinawa islands, an account Beijing disputed.

"These radar illuminations are a dangerous act that went beyond what is necessary for the safe flight of aircraft," Prime Minister Sanae Takaichi told reporters, adding that Japan had lodged a protest with China over Saturday's "extremely regrettable" incident.

Defense Minister Shinjiro Koizumi, meeting with his Australian counterpart Richard Marles in Tokyo, said Japan would respond "resolutely and calmly" to China's conduct in order to maintain regional peace and stability.

But a Chinese navy spokesperson, Colonel Wang Xuemeng, said Japanese aircraft had repeatedly approached and disrupted the Chinese navy as it was conducting previously announced carrier-based flight training east of the Miyako Strait.

CHINA-JAPAN TIES STRAINED OVER TAIWAN

The encounters near islands claimed by both Japan and China are the most serious run-ins between the two militaries in years and are likely to further escalate tension between the two East Asian powers.

Relations have soured in the past month since Takaichi warned that Japan could respond to any Chinese military action against Taiwan if it also threatened Japan's security.

Directing a radar beam at another aircraft is a threatening step because it signals a potential attack and may force the targeted plane to take evasive action. Japan did not say whether the Chinese had locked on their planes or how Japan's aircraft responded.

Wang, in a statement on official social media channels, countered that Japan's statement was erroneous and its actions had seriously endangered flight safety.

"We solemnly demand that the Japanese side immediately stop slandering and smearing and strictly restrain front-line actions," Wang said. "The Chinese Navy will take necessary measures in accordance with the law to resolutely safeguard its own security and legitimate rights and interests."

Australia's Marles, at a press conference with Koizumi after discussions on deepening defence cooperation, said, "We are deeply concerned by the actions of China in the last 24 hours. We will continue to work with Japan and stand with Japan in upholding that rules-based order."

As China-Japan tensions over Taiwan have mounted, Beijing advised its citizens not to travel to Japan and paused plans to restart seafood imports suspended after Japan released treated water from the crippled Fukushima nuclear plant.

China claims democratically governed Taiwan and has ramped up military and political pressure against the island, whose government rejects Beijing's territorial claims. Taiwan lies just 110 km (70 miles) from Japan's westernmost island, Yonaguni.

Japan hosts the biggest overseas concentration of U.S. military power, including warships, aircraft and thousands of U.S. Marines in Okinawa.

The U.S. State Department and the U.S. Embassy in Tokyo did not immediately respond to requests for comment on Japan's claims about China's use of its radar.

TRUMP SILENT, CHINA STEPS UP MILITARY ACTIVITY

U.S. Ambassador to Japan George Glass has publicly expressed support for Japan in several social media posts since the diplomatic dispute began, but President Donald Trump and other senior U.S. officials have remained silent.

The Trump administration said in a strategy document on Friday that it aims to prevent conflict with China over Taiwan and the South China Sea by building up U.S. and allies' military power.

Trump, who plans to visit Beijing next year for trade talks, telephoned Takaichi last month, urging her not to escalate the dispute, people with knowledge of the matter told Reuters.

That call followed a conversation between Trump and Chinese President Xi Jinping, who told Trump that Taiwan's return to China was central to Beijing's vision for the world order, the official Xinhua news agency reported.

Japan said the Chinese J-15 jets involved in the two incidents were launched from China's Liaoning aircraft carrier, which was manoeuvring south of the Okinawan islands with three missile destroyers. Japan said it scrambled F-15 fighters in response to flight operations from the Chinese carrier.

In 2013, Japan said a Chinese warship locked its radar on one of its destroyers in the East China Sea. Three years later, Beijing accused Japanese jets of training their radar on Chinese fighters. In June, Japan said Chinese jets flew dangerously close to one of its patrol aircraft near Okinawa.

On Thursday, China had more than 100 naval and coast guard vessels deployed across East Asian waters at one point, Reuters reported, citing sources and intelligence reports.

Taiwan's government described that build-up as posing a threat to the Indo-Pacific region.

On Sunday, Taiwan's coast guard said it was monitoring drills by three Chinese maritime safety ships on the western side of the Taiwan Strait's median line but that the situation in the waters surrounding Taiwan was "normal".

Chinese state media said the search-and-rescue drills were in the central waters of the strait, patrolling "high-traffic areas, and areas with frequent accidents".

Taiwan's coast guard said China was using "misleading and false wording" about what it was doing, with the aim of harassing Taiwan and carrying out psychological warfare.

China says it alone exercises sovereignty and jurisdiction over the strait, a major trade route for about half of global container ships. The United States and Taiwan say the strait is an international waterway.

(Reporting by Tim Kelly, Nobuhiro Kubo and Kiyoshi Takenaka in Tokyo, and David Kirton in Shenzhen; Additional reporting by Ben Blanchard in Taipei and Ahmed Aboulenein in Washington; Editing by Diane Craft and William Mallard)