US President Donald Trump on Wednesday said he would be meeting with North Korean leader Kim Jong-un later this year, days after scaling back joint US-South Korea military drills.

Trump also provided an unusually specific assessment of Pyongyang's nuclear capabilities, claiming the country now has "57 very power nuclear weapons".

Trump was responding to questions from reporters about his recent hints regarding communications with the North Korean leader, while on a tour of a new helipad at the White House.

While he refused to say whether the pair were exchanging letters, he said he gets "along with him very well."

"And you know what, the fact that I get along with him, that's a good thing not a bad thing. He has 57 very powerful nuclear weapons. Should have never allowed it to happen," he said, adding: "If I were president, I wouldn't have allowed it. But he's got them."