Chinese fighter jets flew unusually close to Japanese military patrol planes over the weekend as two Chinese aircraft carriers operated in the Pacific Ocean for the first time, Japan's defence ministry said late on Wednesday.
On Saturday, a Chinese J-15 jet from the aircraft carrier Shandong chased a Japanese P-3C patrol aircraft for about 40 minutes, the ministry said.
While Beijing said its military activities were, "fully in line with international law" and asked Japan to stop its "dangerous" reconnaissance, Japanese and US officials have seen the jets' actions as another sign of the Chinese military's growing assertiveness beyond its borders.
Tokyo has, "expressed serious concern...and solemnly requested prevention of recurrence" to Beijing, Chief Cabinet Secretary Yoshimasa Hayashi said on Thursday, referring to the June 7-8 incidents in which Japan said Chinese jets flew as close as 45 metres to Japanese planes.
On Sunday, a J-15 chased a P-3C for 80 minutes, crossing in front of the Japanese aircraft at a distance of only 900 metres (2,950 feet), it said.
At one point on both days, a Chinese J-15 flew as close as 45 metres to a Japanese aircraft, the ministry said.
The P-3C aircraft, belonging to Japan's Maritime Self-Defense Force based in the island of Okinawa, were conducting surveillance over international waters in the Pacific, the ministry said.
"Such abnormal approaches by Chinese military aircraft could potentially cause accidental collisions, and we have expressed serious concern and strongly requested prevention of recurrence," the ministry said, attaching close-up images of the J-15 jet it took on Sunday.
In response, China's foreign ministry spokesperson Lin Jian told a regular press conference that, "the close-in reconnaissance by Japanese ships and planes of China's normal military activities is the root cause of the risk to maritime and air security."
"The Chinese side urges the Japanese side to stop such dangerous behaviour."
Earlier this week, Tokyo said the Shandong and another Chinese carrier, the Liaoning, were conducting simultaneous operations in the Pacific for the first time. Beijing has said the operations were a "routine training" exercise that did not target specific countries.
The Chinese presence in the sea and airspace in the southeast of the Japanese island chain has put Tokyo and its ally Washington on heightened alert, as Japan pursues its biggest military buildup since World War Two in the wake of the intensifying security environment in East Asia, including over Taiwan.
"Our sense of urgency is growing," General Yoshihide Yoshida, Chief of Staff of Japan's Joint Staff, told a briefing.
"As evident in the South China Sea, the Chinese military has unilaterally changed the status quo through force wherever their military influence extends...we will maintain a deterrent posture not to allow these actions normalised," added Yoshida, Japan's highest-ranking uniformed officer.
In 2014, Tokyo said it spotted Chinese military aircraft flying as close as 30 metres to its military aircraft over the East China Sea and protested to Beijing.
(Reporting by Kantaro Komiya and Nobuhiro Kubo; Editing by Christian Schmollinger)