North Korea is capable of conducting another nuclear test at any time, South Korean spy agency chief said Friday, citing activity at the country's nuclear site.

"Human and vehicle activities remain active in the second shaft at the North's Punggye-ri nuclear test site even during the winter, and the third shaft is capable of further testing at any time," Lee Byoung-ho, director of the National Intelligence Service (NIS), was quoted as telling the parliamentary intelligence committee by lawmakers. 

"North Korea is only weighing when to make another provocation based on political situations surrounding South Korea and the United States."

Lee also said that the North conducted a land-based ejection test of a submarine-launched ballistic missile at its Sinpo Shipyard earlier this month.

This year, Pyongyang carried out its fourth and fifth nuclear tests, together with tests of more than 20 missiles, including SLBMs and Musudan intermediate-range ballistic missiles capable of reaching the U.S. territory of Guam.

He also said North Korean leader Kim Jong-un threatened to turn South Korea's presidential office of Cheong Wa Dae into "a sea of fire" during his recent inspection of a military drill. (Yonhap)