North Korean leader Kim Jong-un has reportedly executed 15 top officials in the reclusive nation, Seoul's spy agency has said.

According to South Korea's Yonhap news agency, the National Intelligence Service (NIS) briefed lawmakers of the country about the executions in a closed-door meeting.

The officials who were executed include people from deputy ministerial level.

While some of them were accused of leaking state secrets, North Korea's vice forestry minister was punished for allegedly questioning the regime's forestation plans.

"In March, four members of North Korea's Unhasu Orchestra were also executed on charges of espionage," the report cited Shin Kyoung-min of the main opposition New Politics Alliance for Democracy as saying.

Four people from an orchestra have also faced the death penalty for purportedly working against the North Korean leader Kim and his family members.

If confirmed, this will not be the first time that North Korea, ruled by the Kim dynasty with an iron fist for several decades, has conducted mass executions. The secretive regime has been accused of using such methods to instill fear among government authorities and the public to reaffirm the ruler's firm grip over the country.