Trump, while airing his views on U.S. foreign policy, had suggested in an interview with The New York Times last week that he was not opposed to Tokyo and Seoul building its own nuclear arsenal as a deterrent against regional rivals.
Trump had made the comment in the context of a larger proposal – both Japan and South Korea aren't paying enough for the defense of their countries, although experts have said the allegations aren't true.
The two countries host tens of thousands of U.S. troops on military bases.
White House spokesman Josh Earnest told reporters Wednesday Trump's suggestion Japan and South Korea ought to nuclearize would be destabilizing.
Trump's insistence U.S. ally South Korea acquire nuclear weapons is inconsistent with decades-long policy, the White House said.
The Republican presidential candidate's view on nukes also contradicts other policies long supported by the international community, Earnest said.
It would be difficult to imagine justifying North Korea's nuclear weapons development, and promoting an arms race would be ridiculous, the spokesman added, according to South Korean newspaper Hankyoreh.
Asian officials and media were also questioning Trump's worldview and his general qualifications for the presidency.
Both the Japanese and South Korean governments are of the opinion the military alliance with the United States is crucial for regional security.
South Korean newspaper JoongAng Ilbo stated in an editorial Trump's call for a removal of U.S. troops was "shocking," and were he to become president he would have an impact on the long-term alliance between Seoul and Washington.
In Japan, Tokyo chief cabinet secretary Yoshihide Suga said the country has no intention to develop nuclear weapons, The New York Times reported.