U.S. Republican presidential candidate Donald Trump insisted Sunday that allies should pay 100 percent of the stationing cost for American troops and the U.S. should end the protection offered unless they agree to do so.

"We right now defend Japan. Japan pays us a small fraction of the cost, a very small fraction. I want them to pay us at least the cost," Trump said in an interview with CNN. "It's actually less than 50 percent. But a general got on and said 50 percent recently. But, even if it was 50 percent, why aren't they paying us 100 percent?"

Trump was talking about Japan and made no mention of South Korea, but the 50 percent part appeared to be about Seoul's cost-sharing because the "general" Trump referred to is believed to be new U.S. Forces Korea Commander Vincent Brooks.

In a Senate confirmation hearing in April, Brooks said that South Korea currently pays about half the cost, about $900 million a year, to help finance the stationing of some 28,500 troops, and that it would cost more to keep those troops stationed in the U.S. than it does in Korea.

Trump insisted that 50 percent is far from enough.

"Of course they should pay 100 percent. You're talking about billions and billions of dollars, and you're talking about worse than that. You're talking about World War III. Somebody attacks Japan, and we end up in World War III," he said on CNN.

He also reiterated that the U.S. should be prepared to end the protection of allies.

"You have to be prepared to walk from a deal. You can't go in there saying -- like Hillary said, 'We will never let our partners down. We will never, never, never.' OK, that's wonderful, except, you know what? If I'm Japan, I say good. We'll keep paying the 50 percent," Trump said.

"You have to be prepared to walk ... these are very smart people we're dealing with, OK? They've been ripping us off for a long time," he said.

Trump has even suggested that South Korea and Japan develop their own nuclear weapons for self-defense so as to reduce U.S. security burdens.

On Sunday, Trump suggested he wouldn't oppose the allies going nuclear, saying "That's up to them. It's not up to me. It's up to them."

Maximizing U.S. interests through negotiation is the No. 1 point in Trump's "America First" foreign policy. Trump and aides have repeatedly emphasized the businessman is an excellent negotiator and is ready to use the skill to regain American interests lost under Democratic administrations.

Trump has even expressed a willingness to negotiate with North Korea's leader, saying in a media interview, "I would speak to him. I would have no problem speaking to him." The remark also sparked criticism that a meeting with the North would end up bolstering the dictator.

On Friday, Trump reiterated the willingness to talk to the North.

"They said, 'Would you mind having negotiations with North Korea?' No problem. Who the hell cares? You have a negotiation. I'm not going there. But you have a negotiation. They say, 'We will never talk; we will never talk.' How stupid are these people," Trump said during a campaign rally in California Friday.

"Who knows if the talks work. Maybe they will. Maybe they won't. They probably will, if you want to know the truth," he said. "I'm not talking from weakness, folks. I know all about negotiating from weakness and from strength."

His Democratic rival Hillary Clinton has strongly criticized Trump for belittling allies, stressing that the U.S. is stronger and safer thanks to the "power of allies." She also accused Trump of having "bizarre fascination with dictators and strong men who have no love for America." (Yonhap)