WASHINGTON, Oct 27 (AFP) - Russia's invasion of Ukraine highlights the "acute threat" posed by Moscow, but China is the most consequential challenge for the United States, the Pentagon said on Thursday (Oct 27).

The dangers are both conventional - Moscow's aggression toward its neighbours and Beijing's efforts to gain control of Taiwan - and nuclear, with Russia possessing an extensive arsenal and China's stocks of atomic weapons growing fast.

US Defense Secretary Lloyd Austin highlighted the different challenges posed by China and Russia as he unveiled the unclassified versions of several military strategy documents.

China "is the only competitor out there with both the intent to reshape the international order, and increasingly the power to do so", Austin said.

"Unlike China, Russia can't systemically challenge the United States over the long term. But Russian aggression does pose an immediate and sharp threat."

The National Defense Strategy, which was released on Thursday, likewise places the primary emphasis on China.

Beijing is seeking to "refashion the Indo-Pacific region and the international system to suit its interests and authoritarian preferences", it says, describing this dynamic as "the most comprehensive and serious challenge to US national security".

The strategy says Chinese rhetoric about and "coercive activity" toward self-ruled Taiwan - which Beijing has vowed to take control of, by force if necessary - is a destabilising factor that risks miscalculation and threatens peace in the area.

As for Russia, it says the "acute threat" posed by Moscow has been most recently demonstrated by Moscow's February invasion of Ukraine.