President Donald Trump's administration could pursue development of new nuclear weaponry and explicitly leave open the possibility of nuclear retaliation for major non-nuclear attacks, if a leaked draft policy document becomes reality.

The Pentagon did not comment on the document, which was published by the Huffington Post website and prompted sharp criticism from arms control experts, who voiced concerns it could raise the risks of nuclear war.

The Defense Department said on Friday it did not discuss "pre-decision, draft copies of strategies and reviews."

"The Nuclear Posture Review has not been completed and will ultimately be reviewed and approved by the President and the Secretary of Defense," the Pentagon said in a statement.

One source familiar with the document told Reuters the draft was authentic, but did not say whether it was the same version that will be presented to Trump for approval.

The Republican Trump's predecessor, Democrat Barack Obama, declared his intent to reduce the role of nuclear weapons in his Nuclear Posture Review in 2010, the last time the policy document was crafted.

The Trump administration's draft document, said, however, that Obama-era assumptions of a world where nuclear weapons were less relevant proved incorrect.

"The world is more dangerous, not less," it said.

It more readily embraces the role of nuclear weapons as a deterrent to adversaries, and, as expected, backs a costly modernization of the aging U.S. nuclear arsenal.

The Congressional Budget Office has estimated that modernizing and maintaining the U.S. nuclear arsenal over the next 30 years will cost more than $1.2 trillion.

The document sought to put those costs in perspective, noting that maintenance of the existing stockpile would account for nearly half the projected costs. An effective nuclear deterrent was also less expensive than war, it said.