Donald Trump's administration is to review whether the US will renew its policy of a world without nuclear weapons.
Christopher Ford, the National Security Council's senior director for weapons of mass destruction and counter-proliferation, said an assessment of US policy will examine whether the aim was "realistic".
“Like all administrations we’re reviewing policy across the board, and that necessarily includes whether or not the goal of a world without nuclear weapons is in fact a realistic objective, especially in the near to medium term, in the light of current trends in the international security environment,” he told the Carnegie International Nuclear Policy Conference.
“It’s too early to say what the answers will be...looking at things with fresh eyes is not saying we will necessarily end up with different positions.”
Mr Ford said there was a “tension” between the goal of nuclear disarmament and the security requirements of the US and its allies.
He argued that the “headspace” for reducing nuclear arsenals had diminished in the years since the Cold War and cuts by the US and Russia seemed unlikely while other nuclear states continue development.
Mr Trump “will not accept a second place position in the nuclear weapons arena” but is open to broader engagement with Russia on the issue, Mr Ford said.
He added that the current “threat environment” had changed substantially from when the review that established America’s current aims took place under Barack Obama in 2010.
The nuclear adviser said the Trump administration would continue American opposition to a “dangerous and misbegotten” proposed treaty to ban nuclear weapons.
UN member states voted overwhelmingly to start negotiations on a “legally binding instrument to prohibit nuclear weapons, leading towards their total elimination” last year.
A conference on the issue will be held in New York starting on 27 March but the move was opposed by nuclear powers including the US, Britain, Russia, France and Israel.
Mr Trump has not made any official policy statement on nuclear weapons but has touched on the issue repeatedly in his speeches and tweets.
Questioned about his warm statements towards Vladimir Putin at a press conference in February, the President warned that war between the US and Russia would be a “nuclear holocaust like no other”.
Mr Trump has repeatedly hit out at a “dangerous” landmark agreement struck with Iran to limit its capability, accusing the country of being the “number one terrorist state”.
But Mr Ford said that unless otherwise decided, the US would adhere to the terms of the Iran nuclear deal.
Mr Trump has also hit out at North Korea in recent days, accusing Pyongyang of “behaving very badly” with continued efforts to develop a long-range nuclear weapon.
Appointed as Mr Trump's top nuclear advisor, Mr Ford was previously chief council for the Senate Foreign Relations Committee and worked in the bureau of arms control and international security under George W Bush.
Shortly after his inauguration in 2009, Mr Obama declared his ultimate aim of a world without nuclear weapons, saying their spread could “lead to the extermination of any city on the planet”.
In a historic visit to Hiroshima last year, he told survivors of the atomic bombing: “Among those nations like my own that hold nuclear stockpiles, we must have the courage to escape the logic of fear and pursue a world without them.
“We may not realise this goal in my lifetime but persistent effort can roll back the possibility of catastrophe.”
Mr Obama was the first serving American President to visit the Japanese city, where the US dropped its first atomic bomb in 1945, killing an estimated 140,000 people in the initial blast and devastating radiation.
