North Korea began new excavation at the Punggye-ri nuclear test site last month, South Korea’s Joongang Ilbo reported Friday, citing an unnamed South Korean government official.

Excavation has started at another location in addition to the three existing tunnels used for nuclear testing. The government source did not reveal the precise location of the new excavation work.

According to the source, while it is a fact that there is presently quick movement of personnel and vehicles, it is unknown when the excavation began or if the new excavation is a tunnel for nuclear testing or merely intended for storage purposes.