What you need to know about the possible US-North Korea summit

SEOUL, South Korea -- U.S. and North Korean officials are charging ahead with negotiations in multiple locations to set a joint agenda and lay groundwork for the June 12 summit in Singapore between President Donald Trump and Kim Jong Un.

Beijing to New York

Kim Yong Chol, a former North Korean spy chief and senior official, and his aide, Choe Kang Il, head of North Korea's Ministry of People's Security, are expected to meet Secretary of State Mike Pompeo in the U.S. this week. The pair arrived in Beijing on Tuesday, Yonhap, the South Korean news agency, reported.

Trump tweeted Tuesday morning that Kim Yong Chol was "heading now to New York."

Kim Yong Chol serves as vice chairman of the Central Committee of North Korea's Worker's party, which faces independent sanctions from the U.S. government. He and Pompeo met twice in Pyongyang during Pompeo's first visit, March 31 to April 1, and then again on May 9, when the U.S. secretary of state accompanied the release of three Americans held captive in North Korea.

President Trump will meet with Prime Minister Shinzo Abe of Japan on June 7th at the White House.

Singapore

In Singapore, delegations from Washington and Pyongyang are working out logistics -- where the two heads of state will meet, which officials are to hold how many meetings, security issues and how much will be open to the press.

Trump said on Twitter that the summit could take longer than one day. Pompeo, earlier this month, said after returning from Pyongyang that "in the event that there is more to discuss, there'll be an opportunity for it to extend into the second day as well."

Kim Chang Son, a top aide to Kim Jong Un at the State Affairs Commission and known as the leader's de facto chief of staff, arrived in Singapore Monday night. Kim, mainly in charge of protocol matters for the ruling Kim family, is to meet the U.S. delegation led by White House Deputy Chief of Staff for Operations Joe Hagin, adding weight that the on-again, off-again, back-on-again June 12 summit is more likely to happen.

Panmunjom

U.S. diplomatic officials with expertise in nuclear issues are talking to the Pyongyang team led by Choe Son Hui, vice foreign minister, at Tongilgak, a building inside the North Korean side of Panmunjom.

Sung Kim, the current U.S. ambassador to the Philippines and former chief nuclear envoy, arrived in Seoul on Sunday inquiring as to Pyongyang's level of commitment to denuclearization. After a round of talks on Monday, the two sides met again on Tuesday, presumably to discuss details, including specific timelines, on how the global community will ensure security for Kim's regime if it relinquished its nuclear arsenal.

The United States delegation consists of Kim, Allison Hooker, Director for Korea for the NSC, and Randy Schriver, Assistant Secretary of Defense for Asian and Pacific Security Affairs at the Department of Defense.

Trilateral summit: Moon, Kim, and Trump?

The idea of a trilateral summit -- Trump, Kim and South Korean President Moon Jae-in -- after Trump and Kim speak on June 12 has surfaced in Seoul.

The South Korean government is officially making extra efforts to hush predictions, but a high-level presidential office source told ABC News that leadership is "waiting to see how it turns out," referring to current negotiations between the North and the U.S. "Depending on its outcome, the president could join President Trump and Chairman Kim in Singapore."

Both Koreas said a three-way summit is desirable when the two leaders met for the first time in Panmunjom on April 27.

The day after their second surprise meeting, Moon on Sunday told reporters that "should the North Korea-U.S. summit succeed, I would like to see efforts to formally end the war through a three-way summit of the South, the North and the U.S."

ABC News' Hakyung Kate Lee, Jaesang Lee and Jiweon Park contributed to this report.