The United States expressed strong concerns to China on Saturday over an escalation in regional tensions in the East China Sea, saying it increased the risk of an incident.
The White House, State Department and Pentagon issued statements after China bolstered its claim to islands that Japan says it owns, warning that it would take "defensive emergency measures" against aircraft that failed to identify themselves properly in airspace over them.
"We urge China not to implement its threat to take action against aircraft that do not identify themselves or obey orders from Beijing," said Secretary of State John Kerry.
The White House said the "escalatory development" increased regional tensions and affected U.S. interests and those of its allies.
"We have conveyed our strong concerns to China and are coordinating closely with allies and partners in the region," said Caitlin Hayden, spokeswoman for the White House National Security Council.
The Pentagon said China's move was "a destabilizing attempt to alter the status quo in the region."
It added the Chinese announcement would not "change how the United States conducts military operations in the region."
Tensions in the region are expected to be a topic of discussion when Vice President Joe Biden travels to China, Japan and South Korea in early December.
The United States has not taken a position on sovereignty issues in the regional maritime disputes, but has stressed the need for the free flow of commerce, a reduction in tensions and peace and stability in the region.
Kerry said the United States had urged China to exercise caution and restraint.