China on Sunday lodged a protest with Japan over the illegal entry of a Japanese civilian aircraft into the airspace over the Diaoyu Islands, warning Tokyo to cease provocative actions that could destabilize bilateral relations.

Liu Jinsong, director-general of the Asian Affairs Department of the Foreign Ministry, lodged solemn representations with Yokochi Akira, chief minister of the Japanese embassy in Beijing, regarding the intrusion by Japanese right-wing forces in a civilian aircraft.

Liu urged Tokyo to immediately cease such illegal and infringing activities and to take effective measures to prevent the recurrence of similar incidents.

China Coast Guard vessels on Saturday promptly took necessary control measures in accordance with the law and launched ship-based helicopters to warn and expel a Japanese civilian aircraft illegally entering the airspace over the Diaoyu Islands during a routine patrol in the waters around the islands. However, Japan's Ministry of Defense accused Chinese ship-based helicopters of violating the country's territorial airspace.

Zhang Xiaogang, a spokesman for the Ministry of National Defense, on Sunday rejected such accusation as a distortion of facts, calling it irresponsible.

The Diaoyu Islands and its affiliated islands are China's inherent territory, Zhang reiterated, adding that illegal entry of the Japanese civilian aircraft into the airspace over the islands seriously violated China's territorial sovereignty.

He defended necessary control measures to warn and expel the aircraft by the China Coast Guard as "completely legitimate and legal".

"China demands that Japan strictly restrain the activities of its citizens, stop the provocative acts that complicate the situation in the waters and airspace around the Diaoyu Islands, and avoid bringing unstable and unsafe factors affecting the overall situation of the development of China-Japan relations," Zhang said.

He vowed that China will continue to take effective measures to firmly safeguard national territorial sovereignty and maritime rights and interests.

China Coast Guard spokesman Liu Dejun on Saturday also urged Japan to immediately cease all illegal activities. The China Coast Guard would continue to carry out law enforcement activities to safeguard China's rights and interests in the territorial waters and airspace of the Diaoyu Islands, Liu added.