The Pentagon document released on Friday, known as the Nuclear Posture Review (NPR), argues that developing smaller nuclear weapons would challenge that assumption. Low-yield weapons with a strength of under 20 kilotons are less powerful but are still devastating. The policy also proposes:
Land-based ballistic missiles, submarine-launched missiles, and air-delivered weapons - to be extensively modernised, as begun under ex-President Obama
Proposed modification of some submarine-launched nuclear warheads to give a lower-yield or less powerful detonation
The defence ministry in Beijing said Washington had played up the threat of China's nuclear threat, adding that its own policy was defensive in nature.
"We hope that the United States will abandon its Cold War mentality, earnestly assume its special disarmament responsibilities, correctly understand China's strategic intentions and objectively view China's national defence and military build-up," its statement said.
In the NPR document, the US accused China of "expanding its already considerable nuclear forces" but China defended its policy on Sunday saying it would "resolutely stick to peaceful development and pursue a national defence policy that is defensive in nature".
How did others react?
The Russian foreign ministry accused the US of warmongering, and said it would take "necessary measures" to ensure Russian security.
"From first reading, the confrontational and anti-Russian character of this document leaps out at you," it said in a statement on Saturday.
Foreign Minister Sergei Lavrov expressed "deep disappointment" at the plan.
Iranian Foreign Minister Mohammad Javad Zarif argued the proposals were in violation of the international nuclear non-proliferation treaty.