BEIJING—China outlined plans to shift its armed forces’ focus toward maritime warfare and accused foreign countries of “meddling” in the South China Sea, setting the stage for a confrontation between senior U.S. and Chinese defense officials at a security conference this weekend.

In its first public summary of military strategy, the State Council—China’s cabinet—said the navy will expand its operations from offshore areas to the open seas, while the air force will shift its focus to include offensive operations as well as defense of China’s territory.

The changes were designed to tackle new security challenges, including the U.S. shift of military and other resources to Asia, Japan’s efforts to overhaul its defense policy, and “provocative actions” from neighboring countries in the South China Sea, the State Council said in a white paper on military strategy published Tuesday.

“We will not attack unless we are attacked, but we will surely counterattack if attacked,” the paper said, reaffirming a long-standing commitment to a strategy of “active defense” of Chinese territory and national interests.

The document comes amid growing discord between China and the U.S. over artificial islands that Beijing is building in disputed waters in the face of protestations from Southeast Asian nations with competing maritime claims.