U.S. Secretary of State John Kerry has slammed Donald Trump's suggestion that South Korea and Japan develop their own nuclear weapons for self-defense, saying nothing can be "more volatile" or "more contrary" to peace and stability.

Kerry also said in an interview with PBS on Tuesday that countries around the world are greatly concerned about the Republican front-runner and that wherever he goes as America's top diplomat, he gets questions, "What has happened to your politics?"

"When Donald Trump talked about Korea and Japan going out and getting their own nuclear weapons, I can't think of anything that would be more volatile, more contrary to peace and stability of the region, more contrary to the fundamental commitment of every president since World War II, to try to minimize the risk of nuclear weapons and minimize the number of people who have them," Kerry said.

Trump has come under strong fire for the nuclear armament suggestion that he first made in an interview with the New York Times late last month, arguing that the U.S. is no longer rich enough to defend other countries and suggesting the possibility of allowing the allies to go nuclear is something that "we have to talk about."

U.S. President Barack Obama has also openly criticized Trump, saying the statements "tell us that the person who made the statements doesn't know much about foreign policy or nuclear policy or the Korean Peninsula or the world generally."

Kerry said that Trump has made countries around the world look warily at the U.S.

"There is great anxiety everywhere I go. People say, 'What has happened in the United States? What has happened to your politics?'" he said.

When a moderator said sentiment in Europe is also moving to the right because of the refugee situation, Kerry said, "You see it move to the right, but you don't see people recommending that other countries get nuclear weapons and go out and defend for themselves." (Yonhap)