WASHINGTON -- Former US Ambassador to Republic of Korea Sung Kim on Sunday crossed into the Democratic People's Republic of Korea (DPRK) to talk about the preparation for a summit between leaders of the two nations, local report said.

Sung Kim, a former US ambassador to South Korea and ex-nuclear negotiator, was summoned from his present posting as US Ambassador to the Philippines to talk with Choe Son Hui, DPRK's vice foreign minister, the Washington Post said in a report.

The White House has not yet confirmed the report, which cited a source familiar with the summit between US President Donald Trump and DPRK leader Kim Jong Un on June 12 in Singapore.

Just a day before, South Korean President Moon Jae-in and Kim Jong-un held a surprise meeting on the northern side of the border village Panmunjom, the second inter-Korean summit in a month.