According to South Korea’s intelligence, North Korean leader Kim Jong-un has ordered the execution of 15 people in 2015, including several top officials.

South Korea’s spy agency told a parliamentary meeting on April 29 that they were executed by firing squad on spying charges.

Those killed include two vice ministers who challenged Kim Jong-un over his policies and members of an orchestra, intelligence officials said.

Kim Jong-un purged and executed his once-powerful uncle Chang Song-thaek for treachery in 2013.

South Korean politicians were told that one of the officials killed was a forestry minister who had complained about North Korea’s forestation plan, Yonhap news agency reported.

“Excuses or reasoning doesn’t work for Kim Jong-un, and his style of rule is to push through everything,” said Shin Kyung-min, a member of South Korea’s parliamentary intelligence committee, quoting an intelligence official.

Shin Kyung-min’s office told Reuters news agency that the unnamed official had added that the executions were a “showcase” in response to what Kim Jong-un saw as a challenge to his authority.

Four members of North Korea’s Unhasu Orchestra are also believed to have been executed in March.

Reports say that Kim Jong-un’s wife, Ri Sol-ju was a singer in the orchestra before her marriage.

South Korean politician Lee Cheol-woo told Yonhap that the head of the orchestra had been executed, possibly for leaking family secrets.

There has been no confirmation from North Korea about the executions but Kim Jong-un has purged his opponents before.