The deputy minister-level officials had worked under the recently fired state security chief Kim Won Hong, and are believed to have been executed for making false reports to North Korean leader Kim Jong Un, according to two parliamentarians who had been briefed by South Korea's National Intelligence Service (NIS).
"Kim Won Hong, the state security chief, is in a house arrest situation after an investigation and more than five deputy minister-level officials who worked under him have been executed by anti-aircraft guns," South Korean lawmaker Kim Byung-kee said.
"Additional executions of working-level officials could happen as the investigation carries on further."
The State Security Ministry of North Korea is effectively its intelligence service, and also runs its prison camps and conducts domestic surveillance of party workers and other citizens.
"The ministry controls and monitors the public and party officials. It was detected that false reports were made for Kim Jong Un," Lee Cheol-woo, another lawmaker who was present, added.
"Kim Jong Un was furious by this finding and put Kim Won Hong in a house arrest and ordered execution of his five people."
He said the dictator also ordered the removal of a statue of his father and predecessor, Kim Jong Il, from the Ministry's grounds as punishment.
"Kim Jong Un ordered the statue of Kim Jong Il to be removed from the National Defense Ministry because they don't deserve to have the statue."
Although Pyongyang officially denies the prison camps exist, according to a US Treasury statement, Kim Won Hong directed and managed activities including "beatings, forced starvation, sexual assault, forced abortions, and infanticide" that took place in the system of prison camps.
The Ministry for State Security reports directly to Kim.
Removed from office
In January, Kim fired Kim Won Hong, one of his top lieutenants, according to South Korea's Unification Ministry.
As Minister of State Security, Kim Won Hong oversaw the North Korean agency responsible for running the country's notorious prison camps, rooting out spies in North Korea and conducting counterespionage operations abroad.
Unification Ministry spokesman Jeong Joon-hee said Kim Won Hong was punished for "human rights abuses committed during interrogations at the State Security Department" among other things.
Report: Hundreds executed
A report released at the end of 2016 claims Kim has ordered 340 people to be executed since he came to power in 2011.
The Institute for National Security Strategy, a South Korean think tank's report, "The misgoverning of Kim Jong Un's five years in power," details how the North Korean leader uses executions to tighten his hold on power.
Of those killed, about 140 were senior officers in the country's government, military and ruling Korean Worker's Party.
The gruesome method of execution has also been used by the regime before -- in May 2015, Kim had his Defense Minister Hyon Yong Chol killed with an anti-aircraft gun at a military school in Pyongyang, in front of an audience.
"(It) would have torn his body apart," RAND Corporation senior defense analyst Bruce Bennett told CNN at the time. "And of course Kim made sure the Defense Minister's family was there to see the execution."