Republican presidential candidate Donald Trump’s nuclear policy is “catastrophic”, the White House says, as world powers meet to debate the future of nuclear weapons.

A major nuclear summit in Washington DC is discussing the threat of terrorism and North Korea.

But it was Mr Trump’s comments raising the prospect of returning fire with a nuke if the Islamic State (IS) group was to attack the US that raised concerns.

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“I’m afraid this kind of talk in an election is bluntly irresponsible and is detrimental to our and all of our allies’ security posture,” US Energy Secretary Ernest Moniz said.

The Republican frontrunner also declared that, as president, he would withdraw troops from South Korea and Japan and allow those two countries, as well as others like Saudi Arabia, to develop nukes.

It drew a scathing rebuke from the US deputy national security advisor Ben Rhodes.

“The entire premise of American foreign policy as it relates to nuclear weapons for the last 70 years has been focused on preventing the proliferation of nuclear weapons,” said Mr Rhodes, one of President Barack Obama’s closest aides.

“That has been the position of bipartisan administrations, of everybody who has occupied the Oval Office.

“It would be catastrophic for the United States to shift its position and indicate that we somehow support the proliferation of nuclear weapons.”

Once dismissed out of hand, Mr Trump’s strong showing in the polls has forced diplomats to take his positions increasingly seriously as he gets within striking distance of the Republican presidential nomination.

Trump battles to contain abortion fallout

Meanwhile, Mr Trump’s campaign team continued attempts to contain the fallout from his comments on punishing women for having an abortion, characterising the flap as a “simple misspeak”.

The billionaire businessman rapidly backed down on Wednesday from his statement that women should be punished for having abortions if the procedure is banned in the US.

The comments triggered a flood of rebukes from both sides of the abortion debate, and his campaign tried to address the repercussions.

“You have a presidential candidate that clarified the record not once but twice,” A Trump spokeswoman Katrina Pierson told CNN, describing the initial comments as a “simple misspeak”.

She described Mr Trump as “pro-life with exceptions” and pointed to his two statements that followed the MSNBC interview as an accurate depiction of his views.

“We shouldn’t make this a 24-hour headline when we have things like terrorism going on in the world,” she said.

Mr Trump pulled back from his initial comments within an hour, first issuing a statement that US states should handle abortion issues and later saying doctors who perform abortions are the ones who should be held responsible.

His latest controversy threatened to further erode his standing with women voters, many of whom have been offended by his use of vulgarities and insulting language to describe women during the presidential race.

The abortion flap erupted as Mr Trump campaigned in Wisconsin ahead of the state’s critical primary on Tuesday.

An opinion poll released on Wednesday showed Mr Trump’s top rival, US Senator Ted Cruz of Texas, had moved ahead of him by 10 percentage points in Wisconsin.

– ABC