by Ting Shi
April 15, 2016 — 7:28 AM EDT

The China-U.S. security rivalry over the South China Sea was on full display Friday, as Defense Secretary Ash Carter visited an American aircraft carrier in the disputed waters, right after a top People’s Liberation Army general inspected facilities nearby.

Carter’s trip to the U.S.S. John C. Stennis was one of the most overt demonstrations so far of America’s determination to maintain its role as the chief guarantor of security in the waters of the Asia Pacific. Similarly, the tour by General Fan Changlong -- second-only in military rank behind President Xi Jinping -- represented the highest-level Chinese visit to islands it’s built in the contested South China Sea.

While the exact time and location of Fan’s trip were unclear, the Ministry of National Defense said he led a group of military and local officials on a tour of lighthouses, meteorological stations and a maritime surveillance center in the Spratly Islands. Confirmation of the visit followed appearances by Carter in India and the Philippines, where he announced efforts to strengthen U.S. military ties with China’s neighbors.

“The message is pretty clear: China is giving a tit-for-tat to the U.S., showing it’s not caving in and won’t cave in on the matter,” said Ni Lexiong, director of the Sea Power and Defense Policy Research Institute at the Shanghai University of Political Science and Law. “Fan’s visit was as if to say, ‘I Am here waiting for you.’”

China’s claims to more than four-fifths of the South China Sea have sparked tensions with other Southeast Asian nations including the Philippines and Vietnam. The U.S., which is not a claimant, contends that the militarization of the islands may hinder navigation in waters that carry more than $5 trillion of trade a year.

Joint Patrols

Carter said on Thursday that the U.S. had started joint patrols with the Philippines in the sea and would be keeping nearly 300 troops in the country through the end of the month. The moves come ahead of a key court ruling on a Philippines lawsuit disputing China’s claim over the waters.

“We will continue to stand up for our safety and freedom, for those of our friends and allies and for the values, principles, and rule based order that has benefited so many for so long,” Carter said Friday before leaving for the Stennis. “As long as we remain steadfast in that commitment, as we had for decades, we will continue to ensure the Philippines remain secure and the Asia Pacific remains a region where everyone can rise and prosper.”

Lu Kang, a spokesman for China’s Ministry of Foreign Affairs, said on Friday that the U.S. and Philippines had “poisoned country-to-country relations, intensified regional contradictions and undermined peace and stability in the South China Sea.”

The Chinese defense ministry’s statement made no reference to military facilities on the "relevant islets and reefs" he visited. Fan, who’s vice chairman of China’s Central Military Commission, met soldiers and construction workers. He found construction activities “going smoothly,” with four of five planned lighthouses already in operation.