The area where a 2.3 magnitude earthquake struck 43 km north-northwest of Kilju, North Mangyong Province, at 5:12 a.m. on Friday. (Yonhap)

Three minor earthquakes struck North Korea's northeastern county of Kilju, home to the country's nuclear testing site, but all of them were natural tremors, South Korea's state weather agency said Friday.

The first quake occurred about 38 km north of Kilju at 3:29 a.m., while the second and third ones struck nearby areas at 4:01 a.m. and 5:12 a.m., respectively, with their magnitudes ranging between 2.1 and 2.3, according to the Korea Meteorological Administration.

The KMA said all of them were natural quakes.

Kilju, home to the Punggye-ri nuclear test site where the North conducted all six of its nuclear tests, is prone to earthquakes,

Including Friday's, a total of 19 earthquakes with a magnitude of at least 2.0 happened in the region this year, accounting for more than a quarter of 71 quakes with a 2.0 magnitude or stronger that happened on and around the Korean Peninsula.

As a granite zone, Kilju's ground had originally been stable, but the repeated nuclear tests could have made it unstable, experts say. (Yonhap)