SEOUL (Reuters) - The wedge of sea between Japan, Russia, and the Korean peninsula became a new flashpoint this week, with a regional airspace dispute, a seized fishing boat, and missile tests by North Korea aggravating longstanding tensions.
The patch of ocean is commonly known as the Sea of Japan, but South Korea argues it should be known by the more neutral name the East Sea.
The dispute over the name exemplifies the numerous conflicting interests in the area, which has been the scene of sometimes intense military and political brinkmanship.
The most serious encounter this week came on Tuesday when Russian and Chinese warplanes conducted their first joint long-range air patrol in the Asia-Pacific over the sea, triggering warning shots from South Korean fighter jets and a round of diplomatic protests.
Analysts say the joint patrol is likely the first of many actions by China and Russia to try to send a message that their collaboration will be an increasingly significant factor in the region.
Tuesday's air patrol highlighted conflicting claims over various "air defence identification zones" (ADIZ).
An ADIZ is usually an area where countries may unilaterally demand that foreign aircraft take special steps to identify themselves, according to the International Civil Aviation Organization.
An ADIZ is different from a country's airspace, which usually means the space above its territory, extending 12 nautical miles away from its coastline.
Unlike airspace, there are no international laws that govern air defence identification zones.
Russia said it does not recognise South Korea's air defence identification zone, known as KADIZ, while China said the area where Tuesday's patrol occurred was not territorial airspace and that all countries enjoyed freedom of movement in it.
This week makes a total of 39 cases of foreign military aircraft entering the KADIZ without identifying themselves this year, South Korea's defence ministry said, all of them from China or Russia.
Tuesday's incident escalated after South Korea said one Russian aircraft penetrated South Korean airspace near a tiny chain of islets claimed by both South Korea and Japan.
Russia says its aircraft were never closer than 25 km (15 miles) from the South Korean-controlled islets.
Japan claims its own ADIZ, and says it also scrambled fighter jets to intercept the Russian and Chinese aircraft.
Graphic: East Asian air patrols and zones (https://tmsnrt.rs/2OeSOTc)
South Korea has for decades administered the disputed islets, which it calls Dokdo. Japan calls them Takeshima.
A war of words over their ownership spilled over to the Olympics on Wednesday as Japan criticised a South Korean complaint over a map of Japan on the Tokyo Games website, which showed the islets as a small dot, coloured as Japanese territory.
Artyom Lukin, a professor at Far Eastern Federal University in Vladivostok, said the joint Russian-Chinese exercise, in "one of the most politically sensitive areas in Northeast Asia", was unlikely to have been a coincidence.
"The message is, the Russo-Chinese 'strategic partnership' is now a force to be reckoned with militarily in East Asia," he said.
The region is likely to see "more frequent and increasingly assertive" joint military actions by Russia and China, he said.
China stressed the importance of its military ties with Russia in a 2019 Defence White Paper released on Wednesday.
"The military relationship between China and Russia continues to develop at a high level, enriching the China-Russia comprehensive strategic partnership of coordination for a new era," China said.
On Thursday, North Korea fired two short-range missiles into the sea off its east coast, a test that South Korea criticised as unhelpful in easing tensions on the peninsula.
Also this week, North Korean leader Kim Jong Un inspected a new submarine that he said would soon be operational in the "East Sea of Korea".
On Wednesday, Russia accused North Korea of illegally detaining one of its fishing vessels and its crew in the rich fishing grounds of the sea, and said it would freeze talks with North Korea on fisheries cooperation until the issue was resolved
"This incident could be irritating for Russia, yet will hardly be a major setback for a relationship already under immense strain due to various issues such as sanctions," said Anthony Rinna, a specialist in Korea-Russia relations at Sino-NK, a website that analyses the region.
(Reporting by Josh Smith; Editing by Robert Birsel)