SEOUL, South Korea– A 2.4 magnitude earthquake hit near a North Korean nuclear test site on Thursday, according to South Korea's state weather agency, which analysed the quake as having occurred naturally.

The quake was detected 41 kilometres (25 miles) northwest of Kilju, which is home to the Punggye-ri nuclear test site, Yonhap news agency reported.

The quake was detected at 7:00 pm (1000 GMT) at a depth of 20 kilometres (12 miles), according to the Korea Meteorological Administration.

Between 2006 and 2017, North Korea conducted six nuclear tests at the Punggye-ri facility.

The 2017 nuclear test triggered a much bigger 6.3 magnitude quake that was felt across the border in China.

Kilju has seen a string of small natural earthquakes in recent months.

Citing experts, Yonhap has said the area around Kilju has grown more quake-prone due to North Korea's repeated tests.

- Stockpiles -

At Pyongyang's year-end policy meetings, North Korean leader Kim Jong Un threatened a nuclear attack on the South and called for a build-up of his country's military arsenal ahead of armed conflict that he warned could "break out any time".

Kim also successfully put a spy satellite into orbit late last year, after receiving what Seoul said was Russian help, in exchange for arms transfers for Moscow's war in Ukraine.

The 2017 test sparked global condemnation, leading the United Nations Security Council to unanimously adopt new sanctions that included restrictions on oil shipments.

Monitoring groups estimated the sixth nuclear test had a yield of up to 250 kilotons, which is 16 times the size of the US bomb that destroyed Hiroshima in 1945.

Following the 2017 test, the North claimed it had detonated a hydrogen bomb "of unprecedently big power", saying it marked a "very significant occasion" in achieving the "final goal" of becoming a complete nuclear power.

US intelligence officials estimated in 2018 that Pyongyang had enough fissile material -- the core component of nuclear weapons -- for 65 weapons, and that it produces enough fissile material for 12 additional weapons every year.

A 2021 report from the RAND Corporation projected that North Korea could have more than 200 nuclear weapons and hundreds of ballistic missiles stockpiled by 2027.