New York [USA], Feb. 7 : Three Chinese Coast Guard ships entered waters near a chain of disputed islands claimed both by China and Japan in the East China Sea on Monday.
Japan controls the chain and calls them the Senkaku Islands, while China calls them the Diaoyu Islands.
The development comes just days after U.S. Defense Secretary James Mattis reaffirmed America's commitment to defending Japan and its disputed islands.
According to Japanese broadcaster NHK, protests were lodged with the Chinese Embassy in Tokyo and in Beijing through the Japanese Embassy.
Tensions have flashed numerous times in recent years over the disputed islands, including face-offs between Japanese and Chinese air and naval forces that have been termed dangerous by both sides, reports the CNN.
China's State Oceanic Administration, which oversees the country's Coast Guard, put out a statement late Monday saying the three ships "cruised within China's Diaoyu Islands territorial sea." China's Defense Ministry also confirmed the Coast Guard ship movement.
Japan's Coast Guard said the Chinese vessels spent two hours in Japanese territorial waters. It was the fourth time Chinese ships have entered Japan's waters this year, the Japanese Coast Guard said.
There were 36 such incidents in 2016, it said. During a press conference Saturday in Tokyo, Mattis said the U.S. would defend the islands with Japan. "I made clear that our long-standing policy on the Senkaku Islands stands. The U.S. will continue to recognize Japanese administration of the islands and as such Article 5 of the U.S.-Japan Security Treaty applies," Mattis said in an appearance with Japanese Defense Minister Tomomi Inada.
The US position was reinforced Tuesday in a phone call between Japanese Foreign Minister Fumio Kishida and the new US Secretary of State Rex Tillerson, according to a statement from Japan's Foreign Ministry.
"The United States will be against any unilateral action made to damage the Japanese administration of the Senkaku Islands," Tillerson stated during the call, according to the Japanese statement.
China responded quickly on Saturday to the US stance on the islands, saying it brings instability to the region.