A U.S. Republican House lawmaker has called for the party's presumptive presidential nominee, Donald Trump, to refine his Asia policy, especially his approaches to issues involving North and South Korea.

Rep. Peter King (R-NY) made the remark, speaking about Trump's plan to use Chinese pressure to rein in North Korea and his apparent threat to withdraw troops from South Korea unless the Asian ally agrees to pay more for American defense support.

"I don't think his Asian policy is coherent, because, again, if he does want to get in a trade war with China, he has to explain how that coincides with him wanting to use China against North Korea. If he wants to have leverage over China, how can he be talking about taking troops out of Japan and Korea?" King said on CBS's "Face the Nation."

"Does he know that it costs more to take the troops out than to leave them there? And does he realize that that would just weaken our leverage against China?" the congressman said.

Trump has long called for allies to pay more for U.S. defense support, claiming that the U.S. is protecting wealthy nations in exchange for little. He has even called for Seoul to shoulder 100 percent of the costs for American troop presence, suggesting he could withdraw troops unless it agrees to pay more.

Walid Phares, a top foreign policy adviser to Trump, said in an interview with Yonhap News Agency that it's true Trump wants Seoul to pay more, but his remarks made as a candidate are an expression of principles and details have yet to be worked out.

King also expressed concern about Trump's policy on Russia.

"I'm very concerned about this romance he seems to have with Putin," the congressman said, referring to Russian President Vladimir Putin. "As far as his statement that he wants Russia to take care of what is happening in Syria, that's Barack Obama's policy."

King noted that Trump benefited the party, saying the real-estate tycoon "brought people into the Republican Party," especially "the blue-collar Reagan Democrats, which we had lost over the years."

"But on foreign policy, I want him to make his policy more coherent. I'm endorsing him. I'm going to vote for him. But before I can actively campaign, I have to see a much more coherent foreign policy," King said. (Yonhap)