BEIJING, Dec 4 (Reuters) - China's military on Monday said a U.S. Navy ship illegally entered waters adjacent to the Second Thomas Shoal, a disputed South China Sea atoll that has recently seen several maritime confrontations.
"The U.S. seriously undermined regional peace and stability," a spokesperson for China's Southern Theater of Operations said in a statement, adding that the U.S. disrupted the South China Sea and violated China's sovereignty.
China is in disputes with several of its neighbours over its extensive claims of territorial waters in the South China Sea.
China protests US Navy sailing near South China Sea claims
The U.S. Navy said the USS Gabrielle Giffords, an Independence-class littoral combat ship, was conducting routine operations in international waters in the South China Sea, consistent with international law.
"Every day the U.S. 7th Fleet operates in the South China Sea, as they have for decades," the U.S. Navy said in a statement. "These operations demonstrate we are committed to upholding a free and open Indo-Pacific region."
In recent months, China has had several runs-ins with Philippine vessels, and protested about U.S. ships patrolling disputed areas.
According to the Chinese military, the U.S. ship moved into waters adjacent to what China calls the Renai Reef, also known as Second Thomas Shoal, a part of the Spratly Islands. The Second Thomas Shoal lies in the Philippines' exclusive economic zone, according to an United Nations tribunal ruling in 2016.
The Chinese military spokesperson said the U.S. ship was monitored and followed, and that China's "troops in the theater are on high alert at all times to resolutely defend national sovereignty".
"We will not be deterred from continuing to work alongside our allies and partners in support of our shared vision for a free and open Indo-pacific," the U.S. Navy responded.
On Sunday, the Philippine Coast Guard deployed two of its vessels in the South China Sea after monitoring an "alarming" increase in the number of Chinese maritime militia vessels at a reef within the country's exclusive economic zone.
