July 2 (UPI) -- Chinese Coast Guard boats have been navigating waters near disputed islands in the East China Sea as tensions rise between Beijing and Tokyo over the Senkaku or Diaoyutai Islands.
A total of four Chinese patrol boats traveled near the disputed territory on Thursday, as the Japanese government expressed grave concern over Chinese activities, NHK and Kyodo News reported.
Chinese boats have been detected in Japan's contiguous waters for the 80th consecutive day, according to reports.
"We take the activities of the Chinese side seriously, and have carried out rigorous protests repeatedly through diplomatic channels," Japanese Chief Cabinet Secretary Yoshihide Suga said.
Suga also said Japan has "various options" to "stably maintain and manage" the waters, and a decision could be made from a "strategic perspective."
Chinese boats have been seen in Japan's contiguous waters daily since April, according to the Japanese government. In 2019, a record number of Chinese boats, 1,097 in total, appeared in Japan's contiguous zone for 282 days of the year. A total of 126 Chinese boats were detected in Japan's territorial waters for 32 days last year, the highest number of boats on record since 2013.
Last month, Yasuhide Nakayama, a politician with Japan's ruling Liberal Democratic Party, introduced a bill that could stop Chinese activities in Japanese waters "using all means," including armed force.
China has defended its activities in response to Japanese protests.
"China's determination and will to protect its territorial and sovereign rights remain unchanged," the Chinese foreign ministry recently said. "The attempts by the Japanese side do not change the fact that the Diaoyutai Islands belong to China."
China's Coast Guard recently deployed a 5,500-ton patrol cutter near the islands, according to Beijing.