The agency told a parliamentary meeting on Wednesday that they were executed by firing squad on spying charges.
Those killed include two vice ministers who challenged Mr Kim over his policies and members of an orchestra, intelligence officials said.
Mr Kim purged and executed his once-powerful uncle 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.
Mr Shin`s office told Reuters news agency that the unnamed official had added that the executions were a "showcase" in response to what Mr Kim 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 Mr Kim`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 Mr Kim has purged his opponents before.
In 2013, Mr Kim put his uncle, Chang Song-thaek, to death, along with a group of officials who had been close to him.
Mr Chang was seen as a mentor to Kim Jong-un during the leadership transition from his father Kim Jong-il in 2011.
More about:
