North Korea has been keen to show it has been conforming to both the spirit and the word of the agreement its leader, Kim Jong-un, reached with US President Donald Trump in Singapore earlier this year.
Media and investigators have been invited to oversee the dismantling of missile test sites and facilities.
"Whatever Kim says about his desire for denuclearisation, North Korea continues to produce and deploy nuclear armed missiles, " an analyst for the US Middlebury Institute of International Studies at Monterey says.
SECRET SITE CONSTRUCTION
The Yeongjeo-dong long range missile base in the mountainous interior of North Korea, close to the border with China, appears to have undergone a rapid and radical expansion — indicating the mass production of its latest missile designs and warheads continue apace.
The Yeongjeo-dong missile base and an unreported site clearly remain active, according to the images. And their upgrade can be tracked back over the past year.
Under the nuclear disarmament agreement, the base should have been deactivated.
But, according to the Middlebury Institute report: "Satellite images show that the base remains active. Moreover, in the past year North Korea has significantly expanded a nearby facility (known as Hoejung-ri) that appears to be another missile base."
An administration facility sits at the entrance to the valley containing the two sites.
The report says construction work began on a significant underground facility there last year, with work continuing. Facilities apparent in the photos include hardened and camouflaged drive-through bunkers, concrete helipads and extensive under-mountain tunnelling.
"There are five entrances to underground tunnels that may be used to store missiles," the report states. "Around 2010, North Korea constructed a pair of large drive-through suitable for large ballistic missiles. These shelters are similar to the ones seen at the older portion of the Yeongjeo-dong base."'
Such facilities are intended to house, service and protect mobile ICBM launchers. In the vent of attack, the mobile launchers will disperse into the surrounding country side and hide.
North Korea-US diplomatic efforts have come to a standstill.
The North has rejected demands for what it calls "unilateral" disarmament, and has instead sought unspecified reciprocal US measures in a gradual process.
The US is demanding that North Korea first disclose a full inventory of its nuclear weapons and take other significant denuclearisation steps before winning major outside rewards — such as easing sanctions.
North Korea, for its part, now wants sanctions relief, the end-of-war declaration and other reciprocal measures from the United States, arguing it has taken some steps, like dismantling its nuclear testing facility and releasing American detainees.
North and South Korea have begun to remove landmines and destroy military bunkers at parts of their common border as part of efforts to improve long-strained relations.
President Trump recently said he is likely to hold a second summit with Kim in January or February. Ban said he hopes the summit will occur at a time when the international community feels confident about North Korea's commitment to denuclearisation.