The US accidentally flew a B-52 bomber over territory claimed by China

Last week, a US B-52 bomber accidentally flew over Chinese-claimed territory in the South China Sea, The Wall Street Journal reports.

During the fly over, which was part of routine US missions in the region, one of the bombers accidentally flew within 2 nautical miles of the Cuarteron Reef, which China has been artificially expanding.

The incident led the Chinese to file a formal complaint with the US through the US Embassy.

The US flight over the reef is the latest in a string of incidents in which US and Chinese interests in the South China Sea have collided and led to raised tensions.

On October 27, the US sent the USS Lassen within 12 nautical miles of China's artificially constructed Subi Reef in the Spratly Islands, along with an accompaniment of two surveillance aircraft. This mission was a "freedom of navigation" operation that was intended to demonstrate that the US did not recognize Beijing's extensive maritime claims in the region.

In response to that event, Chinese Foreign Minister Wang Yi called US Secretary of State John Kerry and expressed China's displeasure with the incident.

"The acts by the U.S. naval vessel in the South China Sea harmed mutual trust and provoked regional tensions. China is extremely concerned by this," Wang said, according to Reuters.

And on December 10, in response to US B-52 bombers trespassing into Chinese airspace over the Spratly Islands in the South China Sea, the Chinese Defense Ministry said that such actions were "serious military provocations," the Journal reports.

The Cuarteron Reef is part of the Spraty Islands, which is claimed at least in part by China, Taiwan, Brunei, the Philippines, and Vietnam. The Cuarteron Reef specifically is claimed by both China and the Philippines.

In total, China has reclaimed 231,100 square meters of land on the Cuarteron Reef, according to Center for Strategic and International Studies' Asia Maritime Transparency Initiative. The reef houses two helipads, a possible radar facility, and possible gun or missile sites.

China's actions in the South China Sea risk escalating a series of territorial disputes since Taiwan, Malaysia, Vietnam, and the Philippines also have military bases within the South China Sea.

A number of neighboring countries claim the reefs, islands, and oil and gas deposits in the area: