Japan-China disputed islands
The statement comes after protests spread to dozens of Chinese cities.
US defence secretary Leon Panetta, who is in Tokyo for talks, has called for restraint on both sides.
"A misjudgement on one side or the other could result in violence, and could result in conflict," said Mr Panetta, who is also due to travel to Beijing this week.
''These law enforcement and patrol activities demonstrated China's jurisdiction over the Diaoyu Island and its affiliated islets, achieved the goal of demonstrating China's sovereignty claim and ensured the country's maritime interests," Xiao Huiwu, deputy chief of the headquarters of CMS told Xinhua news agency.
Anti-Japanese protests swept across China over the weekend, with thousands of protesters targeting Japanese-made cars and burning Japanese flags.
On Sunday, hundreds of Chinese protesters faced off against riot police at the Japanese embassy in Beijing.
Japanese Prime Minister Yoshihiko Noda has urged Beijing to take steps to protect Japanese nationals, adding that the authorities in both countries should "remain calm".
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