There were no signs of reactor operation from early December 2018 to early July 2021, the IAEA explains.
But since the beginning of July 2021, there have been indications, including discharges of cooling water, that are consistent with reactor operation.
The assessment is shared by the US-based site 38 North, which analyzes developments in North Korea.
- The timing appears to be a bit strange, given the risk of floods in the coming weeks and months, which could affect the reactor operation, says manager Jenny Town.
Try to reach North Korea
The IAEA report underscores the "urgent" importance of maintaining diplomatic dialogue, according to a source close to the US government.
- We continue to seek dialogue with the DPRK (North Korea) in order to address this activity, and the full spectrum of issues related to nuclear disarmament, the source said.
The IAEA has not been admitted to North Korea since the Pyongyang government expelled its inspectors in 2009. Instead, the body monitors North Korea remotely, mainly via satellite.
Summit with the USA 2019
At the North Korean leader Kim Jong-Un's summit with former US President Donald Trump in Vietnam in 2019, Kim offered to dismantle (the nuclear reactor) Yongbyon in exchange for light sanctions against the country.
However, Trump said no, on the grounds that the reactor was only part of North Korea's nuclear program, and that a closure would not be enough.