On Tuesday, King made an unauthorized crossing into North Korea, the same day a US nuclear-armed ballistic missile submarine visited South Korea for the first time since the 1980s.
"In their daily lives, they couldn't go out for shopping in downtown Pyongyang by themselves, let alone travel abroad," Tae said of other US soldiers who defected decades ago.
"The DMZ remains a very dangerous area due to mines, unexploded ordnance, poor infrastructure and the resident forces of both sides," the UNC said on its website.
The lawyer, who declined to be named due to the sensitivity of the matter, said he was unaware of the status of King's custody or whereabouts after February.
North Korea launched two ballistic missiles eastward early on Wednesday, the Japanese Defense Ministry said.
The person was taking part in a tour to the Joint Security Area, the border village in the demilitarized zone separating the two Koreas.
Kim accuses the US Air Force of intruding into the North's "economic water zone" off the east coast of the Korean peninsula.
"There is no guarantee that a shocking incident where a US air force strategic reconnaissance plane is shot down over the East Sea will not happen," the spokesperson said.
North Korea also vowed it will continue to develop its nuclear capability and strengthen solidarity with other countries that oppose what it called the "US strategy for world supremacy."
Nate Evans, the spokesperson for the US mission to the United Nations, said the United States had called for an open meeting on the launch, which means the proceedings would be streamed live.