Japan has protested after Chinese fighter jets locked radars on Japanese aircraft as tensions between the two nations worsened. Locking radar onto an aircraft is considered a threat because it can signal a potential attack. Japan said there were two such incidents Saturday off its southern Okinawa islands.

A Chinese carrier strike group sailing close to Japan kept up intense air operations on Sunday as it sailed into the Pacific Ocean east of the Okinawa Islands, Japan's Self-Defense Forces said Monday.