New satellite imagery shows what appears to be improvements to the Yeongjeo-dong missile base, a facility located in North Korea's mountainous interior, as well as work on a new facility, Hoejung-ri, 11 kilometers (seven miles) away.
As of August 2018, researchers said North Korea is continuing to construct an extremely large underground facility.
China is the North's most important economic and political partner, but has signed on to United Nations economic sanctions aimed at pressuring leader Kim Jong Un to abandon his drive to develop nuclear weapons and the ballistic missiles to deliver them.
But diplomacy has since come to a halt amid disputes over a U.S. demand that North Korea first produce a full inventory of its nuclear weapons and take other denuclearisation steps before winning significant outside rewards.
In a statement the Pentagon said: "We watch North Korea very closely but we can not discuss intelligence".
He suggested the meeting could happen in January or February and that the USA could continue to enforce the economic sanctions it imposed on North Korea over its weapons program.
John Bolton knew of Huawei arrest before Trump-Xi dinner
U.S. national security officials have said Huawei poses a security risk due to its alleged close links to the Chinese government. Huawei's smaller rival ZTE Corp pleaded guilty previous year to conspiring to evade embargoes by selling US equipment to Iran.
"Whatever Kim says about his desire for denuclearization, North Korea continues to produce and deploy nuclear armed missiles", he told CNN.
During the talks, Kang and Pompeo will discuss issues of mutual concern, including a joint strategy on North Korea, according to South Korean Foreign Ministry spokesman Noh Kyu-duk.
North Korea has expanded a key long-range missile base in the months since a summit between the country's leader Kim Jong Un and US President Donald Trump, according to a report on Wednesday (Dec 5).
"They have not lived up to the commitments so far", Bolton said at The Wall Street Journal's annual CEO Council conference in Washington.
An official at Seoul's presidential Blue House who spoke to JTBC on the condition of anonymity said the South needs an answer by the weekend in order to make plans for a summit, if it is to happen before the end of the year.
One such facility is the missile base near Yeongjeo-dong, a site that has long concerned US and South Korean officials and the subject of the analysis of the new images released Wednesday.
But National Security Adviser John Bolton said Tuesday that there should be another summit with Kim. "These shelters are similar to the ones seen at the older portion of the Yeongjeo-dong base".