BEIJING (Reuters) - South Korea's decision to deploy an advanced U.S. anti-missile defense system does not threaten China's security, a senior U.S. administration official said on Tuesday at the end of a visit to China by U.S. National Security Adviser Susan Rice.

The announcement by South Korea and the United States this month that they would deploy a Terminal High Altitude Area Defence (THAAD) unit has already drawn protests from China that it would destabilize regional security.

The decision is the latest move to squeeze increasingly isolated North Korea, but China worries the system's radar will be able to track its military capabilities. Russia also opposes the deployment.

"It is purely a defensive measure. It is not aimed at any other party other than North Korea and the threat it poses and this defensive weapons system is neither designed nor capable of threatening China's security interests," the official told reporters on a conference call.

South Korea and the United States have said THAAD would only be used in defense against North Korean ballistic missiles.

North Korea has launched a series of missiles in recent months, the latest last week when it fired three ballistic missiles in what it said was a simulated test of preemptive strikes against South Korean ports and airfields used by the U.S. military.

The missiles flew 500-600 km (300-360 miles) into the sea off its east coast and could have hit anywhere in South Korea if the North intended, the South's military said.

North Korea came under the latest round of U.N. Security Council sanctions in March after its fourth nuclear test in January and the launch of a long-range rocket the following month.

Rice also emphasized the importance of all sides implementing U.N. sanctions on North Korea, and was pleased that China said it remained committed to their implementation, said the senior U.S. official who declined to be identified.

(Reporting by Sue-Lin Wong; editing by Ben Blanchard)