TOKYO (AFP) ― Three Chinese coast guard ships sailed through waters off Tokyo-controlled islands in the East China Sea on Saturday, the Japanese coast guard said, the latest such incident in a bitter territorial row between the Asian giants.

The state-owned Chinese vessels entered the 12-nautical-mile territorial waters off Senkaku which China claims and calls Diaoyu at around 9 a.m. and left about two hours later, it said.

Chinese vessels and aircraft have regularly approached the East China Sea archipelago ― thought to harbor vast natural resources ― after Japan nationalized some of the islands in September 2012, setting off the latest spate of incidents in a long-running territorial dispute.

Fears of conflict rose in November when China imposed an air defense identification zone 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 in the skies.

U.S. Defense Secretary Chuck Hagel held talks with his Japanese counterpart Itsunori Onodera last week and warned China against unilateral action to resolve a territorial dispute with Japan or other Asian countries.

China’s defense minister, defending his country’s claim, said on Tuesday that Beijing would not act first to “stir up troubles” over island disputes with its neighbors.