"And I will say this. He is doing the wrong thing ... He's making a big mistake," he said.

Asked what he was going to do with the North, Trump said he doesn't reveal those things.

"I'm not like Obama," Trump said, criticizing his predecessor for announcing his plans to strike the Iraqi city of Mosul in the fight against the militant group Islamic State so as to give adversaries enough time to get prepared for the strikes.

Tensions on the Korean Peninsula have been running high amid speculation that North Korea may conduct its sixth nuclear test or carry out a threatened test of an intercontinental ballistic missile capable of reaching the US around its key anniversaries in April.

The US has sent an aircraft carrier strike group led by USS Carl Vinson toward the Korean Peninsula, rather than executing previously planned port visits to Australia, in a show of force designed to warn the North against additional provocations.

In an interview with the Wall Street Journal, Trump said that the deployment is to deter North Korea from taking further actions.

Trump also said he asked Chinese President Xi Jinping in a phone call to let the North's leader know the US doesn't just have aircraft carriers, but also nuclear submarines.

"You cannot allow a country like that to have nuclear power, nuclear weapons," Trump said during the interview. "That's mass destruction. He doesn't have the delivery systems yet, but he will. In many ways, that's the easiest thing."

Trump told Fox Business that he had extensive talks about North Korea with Xi last week.

"The first thing I brought up was North Korea. I said, 'You've got to help us with North Korea, because we can't allow it. And it's not good for you. And you have a tremendous power because of trade,'" Trump said, referring to last week's talks with Xi in Florida.

"Now, he then explains thousands of years of history with Korea. Not that easy. In other words, not as simple as people would think. They've had tremendous conflict with Korea over the years. Now, his father was in China four times. He was never in China," he said, referring to North Korean leader Kim Jong-un and his late father, Kim Jong-il.

Trump said he again pressed Xi to use trade with the North as leverage.

"I said, 'Look, you have a tremendous power because of trading through the border.' If they don't get food, they don't get, you know, they can't sell their coal. In fact, I hear today two massive coal ships from North Korea were sent back to North Korea, heading to China. They were sent back, which is a very good sign," he said.

Trump said he told Xi that China will "do much better on trade if they help us with North Korea."

Trump said he and Xi had about five hours of one-on-one talks on Thursday and Friday last week.

"I really liked him. We had a great chemistry," he said. "We were going to have a 10 or 15 minute sit-down. It lasted for three hours."

On Wednesday, Trump said that Xi wants to help the US with the North.

"President Xi wants to do the right thing. We had a very good bonding. I think we had a very good chemistry together. I think he wants to help us with North Korea," Trump said during a joint news conference with NATO Secretary General Jens Stoltenberg.

Trump said he told Xi that the way for China to get a good trade deal is to help the US with the North. Unless China provides help, the US would "go it alone," Trump said, adding that "going it alone means going it with lots of other nations."

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.

Four days after the summit talks, Trump and Xi also spoke by phone Tuesday (US Eastern Time).

"Had a very good call last night with the President of China concerning the menace of North Korea," Trump said in a tweet earlier Wednesday.

Chinese state broadcaster CCTV reported earlier that Xi emphasized the importance of a peaceful resolution to the nuclear issue during the call with Trump, and the two sides agreed to strengthen high-level consultations. (Yonhap)