BEIJING (Reuters) - China’s navy carried out drills in the South China Sea to simulate fending off an aerial attack, state media said on Friday, as the country trades barbs with the United States over responsibility for heightened tension in the disputed waterway.

U.S. Secretary of State Mike Pompeo expressed concern during a visit to Beijing on Thursday over China’s efforts to militarize the seas.

His remarks came after a flurry of U.S. activity in the region, including reports last week that U.S. Air Force B-52 bombers had flown near disputed islands that drew a sharp rebuke from China.

China’s navy carried out a simulated missile attack in an unspecified area of the South China Sea using three target drones making flyovers of a ship formation at varying heights, the official army newspaper said.

The drills were part of efforts by a training base, also unspecified, to prepare for real-life combat with aerial targets after China’s leadership said some training failed to prepare troops effectively, it added.

The United States and China have frequently sparred over who is militarizing the South China Sea, with Beijing blaming tension on actions such as the “freedom of navigation” operations by the U.S. navy.

Washington says such operations are necessary to counter China’s efforts to limit nautical movement there.

A U.S. Navy destroyer sailed through waters claimed by China in May just days after the United States withdrew an invitation to it for a major U.S. hosted naval drill.

Critics have said the operations have little impact on Chinese behavior and are largely symbolic.

Pentagon officials have long complained that China has not been candid enough about its rapid military build-up and its use of South China Sea islands to gather intelligence.

In addition to China, Brunei, Malaysia, the Philippines, Taiwan, and Vietnam all have competing claims in the South China Sea.

Strengthening the navy has been a key part of China’s ambitious military modernization overseen by President Xi Jinping, as it seeks to project power far from its shores.

State television on Friday showed pictures of Xi touring a submarine in the northern port city of Qingdao, where was briefed on its weapons systems, chatted with sailors and asked questions about the submarine fleet’s training.