"We talked trade. We talked a lot of things. I said the way you're going to make a good trade deal is to help us with North Korea. Otherwise, we're just going to go it alone. That will be all right, too. But going it alone means going it with lots of other nations," he said. "I think he wants to help. We will see whether or not he does."

Trump cited China's decision to return coal imports from North Korea as an example.

"I really think that China's going to try very hard and has already started. A lot of the coal boats have already been turned back. You saw that yesterday and today. They've been turned back.

The vast amount of coal that comes out of North Korea going to China. They turned back the boats," Trump said.

"That's a big step. So we will see what happens. It may be effective, may not be effective. If it's not effective, we will be effective. I can promise you that," he said. (Yonhap)