BEIJING/WASHINGTON (Reuters) - China said on Friday it would not stand for violations of its territorial waters in the name of freedom of navigation, as the United States considers sailing warships close to China’s artificial islands in the South China Sea.

A U.S. defense official told Reuters on Thursday the United States was considering sending ships to waters inside the 12-nautical-mile zones that China claims as territory around islands it has built in the Spratly chain.

Western media reports quoted U.S. officials as saying the action could take place within a matter of days, but awaited a decision by U.S. President Barack Obama.

The commander of U.S. forces in the Pacific, Admiral Harry Harris, declined to say on Friday whether the United States would carry out the plan. But he made clear it was an option he had presented to Obama and said the United States must carry out freedom of navigation patrols throughout the Asia-Pacific.

“I simply won’t discuss future operations,” Harris told a Washington seminar. “With regards to whether we are going to sail within 12 miles, or fly within 12 miles, of any of the reclaimed islands that China has built in the South China Sea, I will reserve that for later.”

Earlier on Friday, China’s Foreign Ministry spokeswoman Hua Chunying warned against any such patrols.

“We will never allow any country to violate China’s territorial waters and airspace in the Spratly Islands, in the name of protecting freedom of navigation and overflight,” she told a regular news briefing.

“We urge the related parties not to take any provocative actions, and genuinely take a responsible stance on regional peace and stability,” she added.

China claims most of the South China Sea, where The Philippines, Vietnam, Malaysia, Brunei and Taiwan have overlapping claims.

Washington has signaled it does not recognize Beijing’s sovereignty over the several islands China has built on reefs in the Spratly archipelago and says the U.S. navy will continue to operate wherever international law allows.

The issue is central to increasingly tense relations between the United States and China, the world’s two largest economies.

David Shear, the U.S. assistant secretary of defense, told the Senate Armed Services Committee last month there had been no U.S. patrols within 12 miles of the Chinese-claimed islands since 2012.

In May, the Chinese navy issued eight warnings to the crew of a U.S. P8-A Poseidon surveillance aircraft that flew near the islands, according to CNN, which was aboard the U.S. aircraft.

During a visit the Washington by Chinese President Xi Jinping last month, the two sides finalized an agreement aimed at reducing the possibility of aerial clashes.

On the eve of Xi’s visit, the Pentagon said a Chinese aircraft performed an unsafe maneuver during an air intercept of a U.S. spy plane on Sept. 15 over the Yellow Sea.

Harris told the seminar he believed the incident was the result of “poor airmanship” rather than a directive from headquarters in China.