Russia carried out what it said was its first long-range joint air patrol in the Asia-Pacific region with China on Tuesday, a mission that triggered hundreds of warning shots, according to South Korean officials, and a strong protest from Japan.
The flight by two Russian Tu-95 strategic bombers and two Chinese H-6 bombers, backed up according to Korean and Japanese officials by a Russian A-50 early warning plane, marks a notable ramping-up of military cooperation between Beijing and Moscow.
That is something likely to worry politicians from Washington to Tokyo and could complicate relations and raise tension in a region that has for years been overshadowed by hostility between the United States and North Korea.
While troops and naval ships from Russia and China have taken part in joint war games before, they have not, according to Russia's Ministry of Defense, conducted such air patrols in the Asia-Pacific region together until Tuesday.
"The joint patrol was carried out with the aim of deepening Russian-Chinese relations within our all-encompassing partnership, of further increasing cooperation between our armed forces, and of perfecting their capabilities to carry out joint actions and of strengthening global strategic security," the ministry said in a statement.
Seoul and Tokyo, who both scrambled jets to intercept the Russo-Chinese mission, accused Russia and China of violating their airspaces, an allegation Moscow and Beijing denied.
South Korean warplanes fired hundreds of warning shots towards the Russian A-50 military aircraft, defense officials in Seoul said, saying it had entered South Korean airspace.
It was the first time a Russian military aircraft had violated South Korean airspace, an official at the South Korean Ministry of National Defense said in Seoul.
The Russian and Chinese bombers had entered the Korea Air Defense Identification Zone (KADIZ) together early on Tuesday, the South Korean defense ministry said.
The separate Russian A-50 airborne early warning and control aircraft later twice violated South Korean airspace over Dokdo — an island that is controlled by Seoul and claimed by both South Korea and Japan, which calls it Takeshima — just after 9 a.m. (midnight GMT Monday), according to the South Korean military.
Russia's Defense Ministry said it did not recognize South Korea's KADIZ, while the Chinese Foreign Ministry said the area was not territorial airspace and that all countries enjoyed freedom of movement in it.
South Korean fighters did not fire any warning shots toward Russia's two bombers, the Russian defense ministry said in a statement, which made no mention of any A-50 aircraft.
It accused the two South Korean F-16 fighter planes of carrying out "unprofessional manoeuvres" and of crossing the path of the Russian bombers and not communicating with them.
"It was not the first time that South Korean pilots tried unsuccessfully to prevent Russian aircraft from flying over the neutral waters of the Sea of Japan," the Russian ministry said.
If the Russian pilots had felt any threat to their safety, their response would have been swift, it added.
A South Korean defense ministry spokesman did not directly address the Russian accusation of reckless behaviour, but said that South Korea had never said the Tu-95 bombers had violated its airspace.
South Korea's top security adviser, Chung Eui-yong, lodged a strong objection with Nikolai Patrushev, secretary of Russia's Security Council, asking the council to assess the incident and take appropriate action, South Korea's presidential office said.
"We take a very grave view of this situation and, if it is repeated, we will take even stronger action," Chung said, according to South Korea's presidential office.
South Korea's Foreign Ministry summoned Russian Deputy Chief of Mission Maxim Volkov and Chinese Ambassador Qiu Guohong to lodge a stern protest and strongly urge them to prevent a recurrence, said ministry spokesman Kim In-chul.
Separately, Japan, which said it had also scrambled fighter aircraft to intercept the Russian and Chinese planes, lodged a complaint with both South Korea and Russia over the incident, Chief Cabinet Secretary Yoshihide Suga said.
Tokyo criticised South Korea for taking action against a Russian plane over what Japan says is its airspace.
"In light of Japan's stance regarding sovereignty over Takeshima, the fact that the South Korean military aircraft carried out warning shots is totally unacceptable and extremely regrettable," Suga told reporters.
The South Korean jets loosed about 360 rounds of ammunition during the incident, an official at South Korea's Joint Chiefs of Staff (JCS) said.
"The South Korean military took tactical action including dropping flares and firing warning shots," the South Korean Defense Ministry said.
A South Korean defense official said that the Russian aircraft did not respond in any threatening way.
It left South Korean airspace but then entered it again about 20 minutes later, prompting the South Koreans to fire more warning shots.