The US committed "a serious military provocation" by flying two Air Force B-52 bombers over a Chinese-controlled man-made island in the South China Sea, China's Defence Ministry says.
The Americans had suggested the planes had strayed off course.
Chinese officials has accused the US of deliberately raising tensions in the disputed region, where China has been aggressively asserting its claims to virtually all islands, reefs and their surrounding seas. It also reiterated that it would do whatever is necessary to protect China's sovereignty.
The Foreign Ministry took a more diplomatic tone, saying the situation was stable.
The US takes no official stance on sovereignty claims in the strategically crucial South China Sea, through which five trillion dollars trillion in international trade passes each year. However, Washington insists on freedom of navigation and maintains that China's seven newly created islands do not enjoy traditional rights, including a 12-nautical-mile (22-km) territorial limit.
Responding to China's protests, Pentagon spokesman Mark Wright said that the December 10 mission was not a "freedom of navigation" operation and that there was "no intention of flying within 12 nautical miles of any feature," indicating the mission may have strayed off course.
The US uses pre-planned freedom of navigation operations to assert its rights to "innocent passage" in other countries' territorial waters.
"The United States routinely conducts B-52 training missions throughout the region, including over the South China Sea," Mr Wright said. "These missions are designed to maintain readiness and demonstrate our commitment to fly, sail and operate anywhere allowed under international law."
He said the US was "looking into the matter".
China's Defence Ministry demanded that Washington immediately take measures to prevent such incidents and damage to relations between the two nations' armed forces.
"The actions by the US side constitute a serious military provocation and are rendering more complex and even militarising conditions in the South China Sea," the ministry said.
It said Chinese military personnel on the island went on high alert during the overflights by the B-52s and that they issued warnings demanding the aircraft leave the area.
China's latest protest comes amid a simmering dispute over Washington's approval this week of the first arms package in four years offered to Taiwan, Beijing's self-governing rival.
Why are you making commenting on The Herald only available to subscribers?
It should have been a safe space for informed debate, somewhere for readers to discuss issues around the biggest stories of the day, but all too often the below the line comments on most websites have become bogged down by off-topic discussions and abuse.
heraldscotland.com is tackling this problem by allowing only subscribers to comment.
We are doing this to improve the experience for our loyal readers and we believe it will reduce the ability of trolls and troublemakers, who occasionally find their way onto our site, to abuse our journalists and readers. We also hope it will help the comments section fulfil its promise as a part of Scotland's conversation with itself.
We are lucky at The Herald. We are read by an informed, educated readership who can add their knowledge and insights to our stories.
That is invaluable.
We are making the subscriber-only change to support our valued readers, who tell us they don't want the site cluttered up with irrelevant comments, untruths and abuse.
In the past, the journalist’s job was to collect and distribute information to the audience. Technology means that readers can shape a discussion. We look forward to hearing from you on heraldscotland.com
Comments & Moderation
Readers’ comments: You are personally liable for the content of any comments you upload to this website, so please act responsibly. We do not pre-moderate or monitor readers’ comments appearing on our websites, but we do post-moderate in response to complaints we receive or otherwise when a potential problem comes to our attention. You can make a complaint by using the ‘report this post’ link . We may then apply our discretion under the user terms to amend or delete comments.
Post moderation is undertaken full-time 9am-6pm on weekdays, and on a part-time basis outwith those hours.
Read the rules here