Moscow and Beijing see a threat, which doesn't come from the missiles but radars U.S. to monitor Russian and Chinese intercontinental missiles.

Due to a number of limitations the THAAD missile defense system doesn’t directly pose a major risk to Russia and China. However, Moscow and Beijing still see a potential threat, which does not come from the missiles but the system’s radars that would allow U.S. to monitor launches of Russian and Chinese intercontinental missiles. Despite the U.S. and South Korea repeatedly claiming that THAAD poses no threats to China or Russia, and is being deployed to defend the South from North Korean missile launches, Moscow and Beijing still harbor serious concerns about the deployment.