US PRESIDENT Donald Trump’s administration has announced that it will continue much of the Obama administration’s nuclear weapons policy, but take a more aggressive stance toward Russia.

It said that Russia must be convinced it would face “unacceptably dire costs” if it were to threaten even a limited nuclear attack in Europe.

The current review of US nuclear policy does not call for an increase in strategic nuclear weapons — a position that Mr Trump recommended in a tweet shortly before he took office, in which he said that the US “must greatly strengthen and expand its nuclear capability until such time as the world comes to its senses regarding nukes.”

In his State of the Union address on Tuesday, Mr Trump made no mention of expansion, though he said the arsenal must deter acts of aggression.

A 74-page report has summarised the review’s findings, calling North Korea a “clear and grave threat” to the US and its allies.

It asserts that any North Korean nuclear attack against the US or its allies will result in “the end of that regime.”

It also cast China as a potential nuclear adversary, saying the US arsenal is tailored to prevent Beijing from gaining advantage by using its nuclear weapons in Asia, or that “any use of nuclear weapons, however limited, is acceptable.”

In a written statement, Mr Trump said US strategy is designed to make use of nuclear weapons less likely.

It also endorsed adhering to existing arms control agreements, including the New START treaty that limits the US and Russia each to 1,550 strategic nuclear warheads on a maximum of 700 deployed launchers.

The treaty, negotiated under President Barack Obama and effective since 2011, and its weapons limits must be met by Monday.

The US says it expects Russia to comply by Monday’s deadline.

As of Sept. 1, the last date for which official figures are available, Russia was below the launcher limit but slightly above the warhead limit, at 1,561.

“Moscow has repeatedly stated its intention to meet those limits on time, and we have no reason to believe that that won’t be the case,” State Department spokeswoman Heather Nauert said.

Nevertheless, the Trump administration’s view is that Russian policies have the potential for miscalculation, leading to an uncontrolled escalation of conflict in Europe.

The Trump nuclear doctrine breaks with Obama’s in ending his push to reduce the role of nuclear weapons in US defence policy.

Mr Trump would consider using nuclear weapons only in “extreme circumstances,” but sees a deterrent role for these weapons.

The Pentagon’s report points to a Russian doctrine known as “escalate to de-escalate” in which Moscow would threaten to use smaller nuclear weapons in a limited conflict in Europe to compel the US and NATO to back down.

“Recent Russian statements on this evolving nuclear weapons doctrine appear to lower the threshold for Moscow’s first-use of nuclear weapons,” the review said.

The administration proposes a solution: modify long-range ballistic missiles carried by strategic submarines to fit them with smaller-yield nuclear warheads.

John Rood, the undersecretary of defence for policy, said the cost would be partially included in the 2019 budget submitted to Congress later this month.

The Trump administration would also develop a nuclear-armed sea-launched cruise missile, re-establishing a weapon that existed during the Cold War but was retired in 2011 by the Obama administration.