WASHINGTON (Reuters) - U.S. President Donald Trump said on Friday he had given Kim Jong Un a direct phone number and suggested he might call the North Korean leader on Sunday, following their summit in Singapore this week.

“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, without saying who he would be speaking to.

Trump, who has hailed his meeting with Kim on Tuesday as a success that removed the North Korean nuclear threat, told reporters later that he had given Kim a phone number to allow him to reach him directly.

“I can now call him. I can now say, ‘Well, we have a problem.’ I gave him a very direct number. He can now call me if he has any difficulties, I can call him,” Trump said during an impromptu news conference on the White House lawn.

Asked about who he would speak to on Sunday, Trump said: “Well, I’m going to speak to people in North Korea, and I’m going to speak to my people who are over in North Korea.” He did not elaborate.

Trump and Kim issued a joint statement after their meeting that reaffirmed the North’s commitment to “work toward complete denuclearization of the Korean Peninsula,” while the United States undertook to provide security guarantees.

Democratic critics in the United States said the agreement was short on detail and the Republican president had made too many concessions to Kim, whose country is under U.N. sanctions for its nuclear and weapons programs and is widely condemned for human rights abuses.

Trump has said he trusts Kim to follow through as the two countries negotiate dismantling North Korea’s nuclear program.

Critics have assailed Trump for talking warmly of Kim after their meeting. In response to a reporter who suggested on Friday that he was defending Kim’s human rights record, Trump said, “You know why, I don’t want to see a nuclear weapon destroy you and your family ... I want to have a good relationship with North Korea.”

U.S. Defense Secretary Mattis said Trump’s summit with Kim, the first between a sitting U.S. president and a North Korean leader, showed that the past did not have to define the future, but that the U.S. military remained vigilant.

“While a possible new avenue to peace now exists with North Korea, we remain vigilant regarding pursuit of nuclear weapons anywhere in the world,” Mattis said, speaking at a U.S. Naval War College graduation.