The Pentagon says that countering China's rapidly expanding military and an increasingly aggressive Russia are now the U.S. military's top national security priorities, outpacing the threat of terrorism.

A new national defense strategy says that competition with China and Russia has threatened America's military advantage around the world. And it will require increased investment to make U.S. forces more lethal, agile and ready for war.

The document reflects persistent U.S. worries about China's military build-up in the South China Sea and its moves to expand its political and economic influence around the globe. It underscores concerns about Russia's aggressive military moves, including the invasion of Ukraine and involvement in the Syria war.

Defense Secretary Jim Mattis is unveiling the strategy Friday morning.