A Chinese naval submarine noticed in waters near the Japanese-controlled Senkaku Islands in the East China Sea last week was a nuclear-powered attack submarine, Japanese Defense Minister Itsunori Onodera said Monday.
The Shang-class submarine was detected Thursday while submerged just outside Japanese territorial waters near the Senkaku Islands. Tokyo filed a protest with Beijing, which also claims the islands, saying the submarine's presence raised bilateral tensions.
According to the Japanese Defense Ministry, the Shang-class is a new type of attack submarine equipped with ship-to-ship missiles that have a maximum firing range of 40 kilometers as well as torpedoes.
"We are seriously concerned over acts that unilaterally raise tensions. We'll keep our guard up to respond swiftly if a similar incident happens," Onodera told reporters, noting that the Shang-class submarine is capable of loading long-range cruise missiles.
A Defense Ministry source speculated that China may have sent the submarine to test the Japanese Maritime Self-Defense Force's patrolling capabilities.
The sovereignty of the Senkaku Islands, called Diaoyu by Beijing, is a perennial flashpoint in relations between Asia's two largest economies, which otherwise have been recently showing signs of improving.
The latest development has alarmed Japan as it was the first time a Chinese submarine was observed in the so-called contiguous zone around the uninhabited islets. The contiguous zone is a band of water beyond the 12 nautical mile territorial waters surrounding any national territory, it extends out to 24 nautical miles.
China Coast Guard vessels, meanwhile, have frequently entered Japanese waters around the Senkakus as part of China testing its territorial claim to the area.