Story highlights Defense Secretary Ash Carter goes to U.S. aircraft carrier crossing the South China Sea

The Philippines and a number of other countries in Southeast Asia have territorial disputes with China

Carter: "We want to continue upholding stability and security in the region"

Hong Kong (CNN) U.S. Defense Secretary Ash Carter has announced an "enhanced military alliance" between the United States and the Philippines, and expressed concerns over China's activities in the South China Sea.

Carter made the announcement while visiting the Philippines where American and Filipino troops are holding annual joint military drills.

Speaking at a news conference with Philippines Defense Minister Voltaire Gazmin Thursday, Carter said the two countries have been conducting joint patrols in the South China Sea and will increase them going forward to ensure security for the region's waters.

Carter also said U.S. aircraft will remain behind at Clark Air Base after the drills, and 200 airmen will continue joint training, conduct flight operations and lay the foundation for joint air patrols, to complement ongoing maritime patrols.

Read More