The United States is "very concerned about recent actions that have increased tensions between China and Japan and we call for intensified negotiations and diplomatic initiatives.
"The zone should not be implemented, and China should refrain from taking similar unilateral actions elsewhere, particularly in the South China Sea," Kerry said, reiterating that such moves by Beijing would not affect U.S. military operations in the region.
Beijing regards the entire South China Sea and island groups within it as its own and interprets international law as giving it the right to police foreign naval activity there. The Chinese navy is operating with increasing frequency in the South China Sea and around Japan as part of China's development of its blue water navy.
Tensions were highlighted earlier this month when a Chinese warship nearly collided with an American cruiser in the South China Sea. The U.S. Pacific Fleet said the USS Cowpens was operating in international waters and had to maneuver to avoid hitting China's lone aircraft carrier, Liaoning, on Dec. 5.
However, China's Global Times newspaper reported on Monday that the U.S. ship had first harassed the Liaoning and its group of support ships, getting too close to a Chinese naval drill and entering within 30 miles of the Chinese fleet's "inner defense layer."
Along with discussing the maritime security issue, Kerry, who is on his 14th visit to Vietnam since the end of the war in 1975, pressed Vietnamese officials to release political prisoners and improve its human rights record, particularly on religious and Internet freedoms. He said the United States was pleased with limited improvements, but that "Vietnam needs to show continued progress on human rights and freedoms, including freedom of religion, freedom of expression and freedom of association."
Without such reforms, he said members of Congress would likely oppose expanded engagement with Vietnam, including its participation in the Trans Pacific Partnership and the implementation of a recently concluded civilian nuclear agreement.