The United States flew two B-1B Lancer bombers over contested regions of the South China Sea on Friday as part of an effort to assert that the waterway remains international territory despite China’s claims of sovereignty.

China has laid claims over nearly the entirety of the South China Sea, despite overlapping claims from a number of other nations in the region and the United States’ position that the international waters are not subject to China’s rule.  China has rapidly expanded its military presence in the region in recent years, launching as many as 18 new naval vessels since the beginning of 2016, and developing a number of artificial islands they are currently equipping with military personnel and hardware.

China responded to Friday’s flight by accusing the United States of parading its military might in the region under the guise of freedom of navigation.

Chinese Foreign Ministry spokesman Geng Shuang explained to the media that China has no problem with freedom of navigation or overflights of the South and East China Seas, “But China resolutely opposes individual countries using the banner of freedom of navigation and overflight to flaunt military force and harm China’s sovereignty and security,” he said.

The Chinese Defense Ministry also released a short statement indicating that China maintains a watchful eye over the waterway and “effectively monitors relevant countries’ military activities next to China.”

“The Chinese military will resolutely safeguard national sovereignty and security as well as regional peace and stability,” it concluded.

Earlier this week, the USS Stethem, an Arleigh Burke-class missile destroyer, sailed to within 12 nautical miles of China’s claimed Triton Island, again as part of what the U.S. military refers to as a “FONOP” or “freedom-of-navigation operation.”  China responded by deployed fighter jets and their own naval vessels to intercept and observe the U.S. destroyer.

The United States, as well as others in the international community, have accused China of militarizing what they see as international waters, primarily through the development of artificial islands.  These islands have military barracks, runways, and what would appear to be shelters intended to house surface to air missiles that China claims are all intended solely as defensive measures to protect their “sovereign territory.”