NEW YORK -- U.S. President Donald Trump appears poised to keep the diplomatic ball rolling with Pyongyang.

Trump plans to call North Korean leader Kim Jong Un on Sunday to follow up on their summit held Tuesday in Singapore, said the president, who spoke with Fox News on the White House lawn on Friday.

"I'm going to be actually calling North Korea," Trump told Fox News in an interview, when asked what he planned to do on Father's Day.

Later, the president told reporters he had given Kim a telephone number where he could be reached directly.

"He can now call me if he has any difficulties, I can call him. We have communication," Trump said.

Trump said the threat of North Korea -- which former President Barack Obama had told him was the biggest problem that the U.S. faced -- was now over. "I have solved that problem," Trump told reporters. "Now we're getting it memorialized and all, but that problem is largely solved. More importantly than the document, I have a good relationship with Kim Jong Un. "