In a statement from its Foreign Ministry, China warned against “any military acts in our exclusive economic zone without permission,” the state-run Xinhua news agency reported Friday. But virtually all the waters to the west of the Korean Peninsula, where the United States said the exercises would take place, lie within that zone, and American naval traffic is far from uncommon there.

Adding yet more tension to the situation, North’s state-run media also warned that the maneuvers could push the Korean Peninsula closer to “the brink of war.”

The West has hoped that China would use its leverage as the North’s traditional ally to press it to refrain from further attacks, but the Chinese statement on Friday failed even to criticize the North for its shelling on Tuesday of a garrison island that is also home to about 1,600 civilians, mainly fishermen. The attack killed four people...