China on Saturday accused the U.S. of a "serious military provocation" after American B-52 bombers flew near artificial islands built by Beijing in the South China Sea earlier this month.
The Dec. 10 incident put military personnel on the Spratly Islands (which Beijing calls the Nansha Islands) on high alert and prompted them to issue warnings to the Americans to leave what they considered their airspace, Chinese ministry of defense officials told state-run news agency Xinhua.
"The actions by the U.S. side were a serious military provocation, creating complex conditions in the South China Sea and even militarization in the region," ministry officials said.
Pentagon officials told the Wall Street Journal they were investigating why one of two B-52s flew closer to the Cuarteron Reef than planned. It's believed bad weather may have prompted one of the pilots to fly off course, the newspaper reported.
China's actions in the South China Sea have angered others in the region, with Beijing using land reclamation to expand reefs in the area and construct artificial islands, thus extending its maritime territory claims.
The U.S. has refrained from taking sides in the territorial dispute, but has asserted its own military rights to move freely in international airspace and waters.
In October, the U.S. sent a warship into the region as part of a direct challenge to China's territorial claims.
"You don't need to consult with any nation when you are exercising the right of freedom of navigation in international waters," State Department Spokesman John Kirby told reporters at the time.
On Saturday, Chinese officials linked the B-52s with past U.S. attempts to "make a show of force."
"The United States has continuously sent military ships and planes to make a show of force and create tensions in the waters and airspace," China's defense ministry said Saturday. "Such actions have severely threatened the safety of Chinese personnel and facilities as well as peace and stability of the region."
Chinese officials demanded the U.S. "immediately adopt measures to prevent such dangerous actions."
"The Chinese armed forces will take whatever measures necessary to safeguard China's national sovereignty and security as well as peace and stability of the region," they warned.