South China Sea. (File photo)

BEIJING, Feb. 19 -- China said on Friday that it does not intend to pursue militarization of the Nansha Islands in the South China Seaand criticized U.S. air and naval patrols in the region.

China has indisputable sovereignty over the Nansha Islands and their adjacent waters, said Foreign Ministry spokesman Hong Lei, adding "China is serious about its commitment not to pursue militarization of the Nansha Islands."

Hong made the remarks after U.S. State Department spokesman John Kirby said commercial satellite imagery suggested "very recent" placement of missiles on Yongxing Island that goes against China's pledge not to militarize the South China Sea.

"We see no indication that ... this militarization effort, has stopped. And it's doing nothing ... to make the situation there more stable and more secure," Kirby said at a regular news briefing on Thursday.

Hong said that demilitarization in the region is not a matter for just a single country. "There should not be double standards or multi-standards for demilitarization in the South China Sea, and the process requires joint efforts from countries in the region and beyond."

He said the United Statesis strengthening military deployment in the South China Sea and frequently sends military vessels or planes to waters in the South China Sea to conduct close-in reconnaissance against China.

He also accused the United States of sending missile destroyer and strategic bombers into waters and airspace adjacent to the Nansha Islands and had its allies hold targeted joint military exercises or joint cruises in the region.

The U.S. actions have escalated tensions in the South China Sea and constitute the militarization of the South China Sea, said Hong.

Yongxing Island, the largest island in the Xisha Islands group in the South China Sea, is an inherent part of China's territory, he said.

In 1959, the Chinese government set up an administrative office and the ensuing government facilities on the Yongxing Island.

The deployment of defense facilities on Yongxing Island amounts to China exercising its sovereignty and it has been going on for decades, he said, urging the U.S. side to learn the basic facts regarding the South China Sea before commenting on the issue.