New satellite imagery has captured an undisclosed and "very active" nuclear weapons facility in North Korea.
The images, captured by Planet Labs and handed to CNN, show busy activity at a large facility just outside North Korea's capital city of Pyongyang.
Researchers at Middlebury Institute of International Studies believe the site is actively manufacturing and storing nuclear warheads.
Middlebury professor Jeffrey Lewis told CNN the images show "all the signatures" of a North Korean nuclear site - a security perimeter, on-site housing and an underground facility.
"The factory is very active... [the facility] is still making nuclear weapons."
Lewis says the images showed significant vehicle traffic, including cars, trucks and shipping containers.
The discovery comes amid growing hostility between North Korea and the United States, with the dictatorship sending numerous threats to strike the US in recent years.
North Korea successfully tested their first intercontinental ballistic missile in 2017.
According to The Nuclear Threat Initiative, North Korea is also in possession of chemical and biological weapons, including anthrax, smallpox and the plague.
The Arms Control Association is uncertain how many nuclear devices North Korea has.
North Korea withdrew from the Treaty of the Non-Proliferation of Nuclear Weapons in 2003, despite the United States attempts to freeze their nuclear activity in exchange for US resources.
A number of countries have imposed sanctions on North Korea in recent years following nuclear testing.