When asked whether the message concerned the release of three American hostages in North Korea, as had been speculated before the South's delegation arrived in the US, the source denied it, saying that the message is more "comprehensive in content".
"I feel they're approaching this matter with caution and they need time to organize their stance".
"There will be several steps (which) will be necessary to agree on the location and the scope of those discussions". He says that it's in the "very early stages". "We have not heard anything directly back from North Korea although we expect to hear something", he said in the Nigerian capital Abuja.
The United States and North Korea fought on opposite sides of a war in the 1950s, and in the last two decades have been engaged in perhaps the world's most unsafe nuclear standoff, with 30,000 US military personnel stationed just over the border in the South. Kim has pilloried Trump as "senile" and a "dotard". Kim's father Kim Jong Il said in talks with the South in 2000 that he could tolerate their presence.
He was part of a South Korean delegation that met Kim in Pyongyang last week.
"I believe they will honor that commitment", the President said.
But Pence called Kim's offers to cease missile and nuclear testing while not objecting to U.S. -South Korean military exercises during that time.
Kim and South Korean President Moon Jae-in will meet at the truce village of Panmunjom straddling the Korean border, but a venue for the North Korea-U.S. summit has yet to be decided. "So we're determined to pursue that course", McMaster told reporters after briefing the U.N. Security Council on the development. He says Russia, South Korea and Japan will as well.
After a meeting with Kim in Pyongyang last week, a delegation of senior South Korean officials headed to Washington to brief the Americans on the visit.
On Friday, White House press secretary Sarah Huckabee Sanders said the meeting wouldn't take place "until we see concrete actions that match the words and the rhetoric of North Korea".
In Beijing, Mr Xi told Mr Chung that the Korean peninsula faces an opportunity for talks to ease the situation. The meeting, if it brings peace, could stabilize countries like South Korea and China.
North Korea's state media have lauded the thaw in relations with South Korea.
A summit between two nations that have remained in a state of war since the Korean War would be a remarkable turnabout after a year of heightened tensions.