Japan scrambled warplanes on Thursday after four Chinese coastguard ships and a drone aircraft entered territory it claims around disputed islands in the East China Sea, according to Defense Ministry officials.
Tokyo said it was the first time Beijing has used an unmanned aircraft in the long-simmering dispute over the islands, called the Senkaku by Japan and the Diaoyu by China.
Japanese Defense Minister Tomomi Inada said use of the drone aggravated tensions inflamed by what Japan says are a record number of scrambles by its Self-Defense Force aircraft in response to Chinese incursions in the last fiscal year.
“China is escalating the situation unilaterally, and this is totally unacceptable,” Inada said at a press conference.
Japan responded with two F-15 fighter jets along with two early warning aircraft, according to the defense minister.
The Senkaku/Diaoyu chain lies almost 1,900 kilometers (1,180 miles) southwest of the Japanese capital Tokyo.
Although the islands are uninhabited, their ownership would allow for exclusive oil, mineral and fishing rights in the surrounding waters.
Though claims to the island chain date back centuries, the most recent round of tensions began in 2012, when Japan nationalized the islands to ward off a planned sale to Tokyo’s then-governor, a hardline nationalist apparently hoping to develop the islands.
The plan sparked massive anti-Japanese protests across China, and Chinese Coastguard vessels and fishing boats began plying waters around the islands.
In 2013, China declared a formal Air Defense Identification Zone covering airspace over the islands and overlapping with airspace claimed by Japan. The ADIZ declaration required airlines flying over the waters to first notify China.
The move prompted an outcry from Japan and the United States, but a US report last year suggested that it was not being fully enforced.
According to Tokyo’s figures, however, China has not been shy in sending its ships and planes into areas claimed by Japan.
For the fiscal year that ended March 31, Japan said it scrambled aircraft a total of 1,168 times, or on average, a little over three times per day.
Chinese incursions were the reason for 73% of those missions, while Russian incursions accounted for 26%, Japan’s Defense Ministry said in an April report.
CNN’s Brad Lendon and Katie Hunt contributed to this report.