The new United States missile defence system is also proving deeply unpopular in South Korea, where Prime Minister Hwang Kyo-Ahn was Friday egged by angry protestors calling for its retraction.
The trilateral meeting comes amid tough sanctions on North Korea for its fourth nuclear and ballistic missile provocations and the announcement of Seoul and Washington's decision to deploy the of us -led Terminal High Altitude Area Defense (Thaad) system, which has led to a strong backlash from Beijing and Moscow who say it will hurt their security interests.
Protests began three days ago in Seongju, located about 135 miles southeast of Seoul, where residents say the THAAD deployment will ruin the town's economic mainstay, melon farming, and cause health and environmental hazards.
Mr Hwang, accompanied by Defence Minister Han Min Koo and others, visited Seongju to try to explain the decision to deploy the Thaad anti-ballistic missile (ABM) system there but was immediately disrupted by jeers.
The protesters also blocked the entrance to the government compound where Hwang was trapped with a tractor as security guards struggled to keep the crowd at bay. But his suit jacket was tainted by eggs and he evacuated to a town hall office.
During the press conference held in Pyongyang, Ko was quoted by the Korean Central News Agency (KCNA) as saying, "I betrayed my homeland and such betrayal can never be forgiven".
The otherwise restful town has been roiled by angry protests since Wednesday when thousands took to the street carrying banners reading "We absolutely oppose THAAD deployment".
Meanwhile Pyongyang warned that it would use "physical measures" against the system, once it is deployed.
He crossed the river from China into North Korea with his inflatable boat - which he planned to use to ferry back the girls - just after midnight on May 27, but was arrested hours later.
The 53-year-old Ko said that the National Intelligence Service (NIS) of South Korea sent him to the Chinese border city of Dandong to kidnap orphans from North Korea, in lieu of $10,000 for each child.
Tensions have been high since Pyongyang carried out its fourth nuclear test in January, followed by various missile launches that analysts said showed the North was making progress towards being able to strike the USA mainland.
In South Korea, the prime minister holds a largely ceremonial role as the head of the cabinet in a powerful presidential system.
North Korea on Friday paraded a defector accused of involvement in a child abduction plot it says was masterminded by South Korean agents, as Seoul demanded the man's immediate release. He and the cabinet are appointed by the president who serves a single five-year term.