Republican presidential candidate Donald Trump brought up the suggestion of allowing South Korea and Japan to develop their own nuclear weapons "as a negotiating point," a senator considered the top foreign policy adviser to Trump said Thursday.

Sen. Jeff Sessions (R-AL) said in an interview with CNN that the nuclear armament remark came as Trump underscored the point that South Korea and Japan should pay more for U.S. defense support, but that does not mean he advocated the idea.

"With regard to nuclear weapons, he sent Japan and South Korea a message. They're not paying their fair share of their defense and they've got to do more," Sessions said. "He said, well, if you don't want to be under our nuclear umbrella and participate sufficiently, then maybe you need your own nuclear weapons. But he didn't advocate that. He was just using that as a negotiating point."

The issue "would certainly be a matter to be discussed so carefully with our good allies, Japan and Korea, but they need to do more," Sessions said.

Trump has displayed deeply negative views of U.S. security commitments overseas, contending the U.S. should stop being the policeman of the world. The real-estate tycoon has said that the U.S. should be prepared to end protection of allies unless they pay more.

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.

Last week, Trump even expressed a willingness to negotiate with North Korea's leader. But the remark sparked criticism that such a meeting would end up bolstering the dictator.

On Thursday, Trump surpassed the magic number of 1,237 delegates necessary to win the Republican nomination.

In the November election, he is expected to be pitted against former Secretary of State Hillary Clinton who is aspiring to become the first female president of the U.S. (Yonhap)