Three Chinese coastguard ships sailed through disputed waters off Tokyo-controlled islands in the East China Sea Sunday, the latest such incident in a bitter territorial row between the Asian giants.
The Chinese vessels entered the 12-nautical-mile territorial waters off one of the Senkakus, which China claims and calls the Diaoyus, at around 9am and left the area around two hours later, the Japan Coast Guard said.
It was the fifth time this year that state-owned Chinese ships entered the zone and the first in six days.
Chinese vessels and aircraft have regularly approached the East China Sea archipelago -- thought to harbour vast natural resources -- after Japan nationalised some of the islands in September 2012, setting off the latest round in a long-running territorial dispute.
Fears of conflict rose in November when China imposed an air defence identification zone (ADIZ) over the East China Sea and said it required notification from planes crossing the area.
Washington was angered by the move, saying it could lead to confusion high in the skies.
US Secretary of State John Kerry has warned Beijing against unilateral moves to set up a similar air defence zone over the South China Sea, where the Philippines in particular has voiced worries about China’s maritime claims.
Earlier this month, the top US diplomat said the United States would defend Japan against attack including over the disputed islands in the East China Sea.