Washington (CNN) The Pentagon on Thursday ratcheted up rhetoric about China's militarization of islands in the South China Sea, even as the Trump administration presses China for cooperation on North Korea.

When asked by a reporter about the ability of the US to "blow apart" one of China's controversial man-made islands, Lt. Gen. Kenneth McKenzie, director of the Joint Staff, told reporters, "I would just tell you that the United States military has had a lot of experience in the Western Pacific taking down small islands."

His comments come amid growing tension in the hotly contested region, as the US ramps up freedom of navigation operations in response to China's steady militarization of its artificial islands.

The US Navy sailed two warships within 12 nautical miles of the disputed Paracel Islands in the past week, the first time it has used more than one vessel in the operations, which are meant to demonstrate the right of free passage in international waters.

JUST WATCHED The West may be too late to stop Beijing in S. China Sea, says analyst Replay More Videos ... MUST WATCH The West may be too late to stop Beijing in S. China Sea, says analyst 05:13

On Wednesday, Adm. Harry Harris, outgoing head of the US Indo-Pacific Command, said China was the US's "biggest long-term challenge" in the region. "Without focused involvement and engagement by the United States and our allies and partners China will realize its dream of hegemony in Asia," he said.

Read More