Some of the nearest sites are around 50km from the Korean Demilitarized Zone .
A US think-tank says it has identified at least 13 ballistic missile sites in North Korea that have not been declared by Pyongyang.
The Centre for Strategic and International Studies (CSIS) has used satellite imagery and interviews with analysts and North Korean defectors to highlight what it says are locations of operating bases.
None of the missile bases has been acknowledged by North Korea.
It says there is an estimated total of 20 North Korean operating bases undeclared by the country's government.
The United Nations has previously accused North Korea of continuing to develop nuclear and missile programs in violation of international sanctions.
The CSIS report claims that maintenance and infrastructure improvements have been observed at some of the sites, despite ongoing negotiations over denuclearisation.
Sites identified in the CSIS report are scattered in remote, mountainous areas across North Korea which the report says they could be used to house "all classes of ballistic missile". The report says:
"Missile operating bases are not launch facilities. While missiles could be launched from within them in an emergency."
Earlier this month, North Korea threatened to restart the development of its nuclear weapons programme if the United States refused to ease strict sanctions.
North Korean leader Kim Jong Un and US President Donald Trump had pledged to work towards denuclearisation at their landmark June summit in Singapore but the agreement was short on specifics and negotiations have made little headway.
Trump tweeted shortly after the summit that "there is no longer a Nuclear Threat from North Korea".
At the time North Korea declared its nuclear force "complete" and halted missile and nuclear bomb testing earlier this year.
However, Pyongyang has not yet made a concrete declaration of the size or scope of the weapons programmes, or a promise to stop deploying its existing arsenal.
A planned meeting between the US Secretary of State, Mike Pompeo, and a high-level North Korean official, Kim Yong Chol, was cancelled last week, reportedly by North Korea.