Japan's close-range reconnaissance has led to security risks at sea and in the sky, Foreign Ministry spokesman Lin Jian said on Thursday.

Lin made the remarks at a regular news conference, after reports quoted Japan as saying Chinese fighter jets flew "unusually close" to Japanese military patrol planes over the weekend.

Defense departments of China and Japan have maintained communication through existing channels over the reported issue, Lin said.

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"China's activities in relevant waters and airspace are fully in line with international law and international practices," Lin said.

"The close-range reconnaissance the Japanese vessels and aircraft conduct against China's normal military activities is the root cause for maritime and airspace security risks," the spokesman emphasized.

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"We urged the Japanese side to stop such dangerous behavior."

China has confirmed it had recently sent carrier strike groups led by the CNS Liaoning and CNS Shandong for training in the Western Pacific.