- Chinese ships enter contiguous zone near disputed Japanese islands
- First time Chinese vessel has come so close to the islands
A Japanese Navy destroyer detected the Chinese ship as it entered the contiguous zone -- an area stretching 24 nautical miles out from the edge of territorial waters -- around the Senkaku, also known as Diaoyu, islands, at 12.50 a.m. local time Thursday (12.50 p.m. ET Wednesday), Yoshitomo Morii told CNN. This was the first time a Chinese frigate has entered the contiguous zone, he added.
"We're deeply concerned that Chinese naval ships entered the waters contiguous to our Senkaku islands for the first time," Japan's Chief Cabinet Secretary Yoshihide Suga told reporters Thursday.
"We, in coordination with the United States and the international community, strongly demand China not repeat such behaviors that unilaterally heighten tensions."
According to Japanese officials, Foreign Minister Vice Minister Akitaka Saeki summoned China's ambassador, Chen Yonghua, to lodge a protest "with serious concern," and demand that the Chinese military ship leave the area immediately.
Morii said the Chinese ship left the area at 3:05 a.m., after repeated calls for it to do so by the Japanese vessel.
Russian military ships were also detected in the contiguous zone between 9:50 p.m. Wednesday and 3:05 a.m. Thursday local time, but further details were not immediately available, Morii said.
According to Japanese state broadcaster NHK, citing senior Japanese officials, the Chinese ship may have been reacting to the Russian vessel's movement.
Both China and Japan claim ownership of the Senkaku chain, and tensions have flared numerous times in recent years.
In late 2013, China declared an air defense identification zone (ADIZ) over much of the East China Sea
, including the Senkakus, despite objections from Tokyo and Washington.
Japan also has an ADIZ over the islands, which it administers. While the Senkakus are uninhabited, their ownership would allow for exclusive oil, mineral and fishing rights in the surrounding waters.
In mid-2014, Japanese and Chinese jets had a tense standoff in a region where both zones overlap
, with Japan's Defense Minister saying the planes at one point came within 30 feet of each other.
Tension over the island dispute has in the past spilled over into protests and violence
against Japanese-owned businesses in China.
The Senkakus are by no means the only islands whose ownership China disputes. Beijing claims the majority of the South China Sea as part of its territory, which has led to heightened tensions and frequent disputes with its neighbors there