The Trump administration has issued some of its strongest words yet on China's moves in the disputed South China Sea, accusing Beijing of "provocative militarization" of the strategic waterway, according to a top State Department official.

The condemnation of China's push to fortify its outposts and claims in the contested waters comes amid the ongoing North Korean nuclear crisis, which some analysts say has captured the lion's share of the White House's attention. They say this has left Beijing with a freer hand to pursue its goals in the South China Sea.

But Brian Hook, a senior policy adviser to U.S. Secretary of State Rex Tillerson, said Tuesday that the issue had been raised at all diplomatic and security dialogues between the two powers.