The Trump administration plans to loosen constraints on the use of nuclear weapons and develop a new low-yield nuclear warhead for US Trident missiles, according to a former official who has seen the most recent draft of a policy review, The Guardian reports.

Jon Wolfsthal, who was special assistant to Barack Obama on arms control and nonproliferation, said the new nuclear posture review prepared by the Pentagon, envisages a modified version of the Trident D5 submarine-launched missiles with only part of its normal warhead, with the intention of deterring Russia from using tactical warheads in a conflict in Eastern Europe.

The new nuclear policy is significantly more hawkish that the posture adopted by the Obama administration, which sought to reduce the role of nuclear weapons in US defence.

Arms control advocates have voiced alarm at the new proposal to make smaller, more “usable” nuclear weapons, arguing it makes a nuclear war more likely, especially in view of what they see as Donald Trump’s volatility and readiness to brandish the US arsenal in showdowns with the nation’s adversaries.

The NPR also expands the circumstances in which the US might use its nuclear arsenal, to include a response to a non-nuclear attack that caused mass casualties, or was aimed at critical infrastructure or nuclear command and control sites.

The nuclear posture review (NPR), the first in eight years, is expected to be published after Donald Trump’s State of the Union speech at the end of January.

Wolfsthal, who has reviewed what he understands to be the final draft of the review, said it states that the US will start work on reintroducing a sea-launched nuclear cruise missile, as a counter to a new ground-launched cruise missile the US has accused Russia of developing in violation of the 1987 Intermediate-Range Nuclear Forces (INF) treaty.