Tokyo (CNN) -- Japan scrambled fighter jets after a Chinese plane was seen Thursday near small islands in the East China Sea that are claimed by both countries.
This is the first time the dispute over the islands, which Japan calls Senkaku and China refers to as Diaoyu, has involved aircraft.
Chinese government ships have repeatedly entered the waters around the remote, rocky islands since the Japanese government announced in September it was buying several of the islands from private owners.
Japanese Coast Guard vessels have engaged in games of cat and mouse with the Chinese ships, with both sides broadcasting messages to one another insisting they have territorial sovereignty over the area.
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On Thursday morning, a Japanese Coast Guard patrol vessel spotted the Chinese government plane in airspace around the islands, Chief Cabinet Secretary Osamu Fujimura said.
Japanese Self Defense Force sent four F-15 jets and another aircraft to the area, Fujimura said, describing the Chinese plane's entry into the area as "extremely regrettable." Japan has lodged a protest with the Chinese government through diplomatic channels, he said.
The Japanese government's acquisition of the islands in September also set off several days of violent anti-Japanese protests across China and soured economic ties between the two Asian nations.
There was no immediate reaction from China about the incident.