Russia and China have denied media reports indicating that the nations deployed additional military forces to North Korea's borders as tensions mount with the U.S.
China conducted joint air and land drills near its unstable border with Myanmar as Beijing stressed national security.
The Asia Maritime Transparency Initiative (AMTI) said the work on Fiery Cross, Subi and Mischief Reefs in the Spratly Islands included naval, air, radar and defensive facilities.
China has been bombing mock U.S. military bases and vessels and could strike personnel stationed in Japan without sufficient warning.
Diplomats briefed on latest Western intelligence assessments say Beijing is pursuing efforts to dominate its maritime 'backyard.'
The Kremlin is not concerned by a reported border deployment but parliament promises response.
The exercise will focus on control of the waters despite a U.N. ruling against China.
China's building spree on remote islands in the South China Sea has its neighbors worried and turning to Washington.
Will China's increased commitment to the peacekeeping forces be a blessing or a curse?
Chinese president Xi Jinping made the surprise announcement at a World War II commemoration parade.
The Canadian coffee shop owners are accused of stealing Chinese military secrets