Kim Jong Un, the North Korean leader, ordered the public execution of two senior bureaucrats with an anti-aircraft gun.
South Korean media is suggesting the killings are the start of a "new reign of terror" in the aftermath of a series of recent high-profile defections.
Sources told South Korea's JoongAng Ilbo newspaper that one of the men was identified as Ri Yong Jin, an official in the Education Ministry, who made the mistake of falling asleep in a meeting with Kim.
"He incurred the wrath of Kim after he dozed off during a meeting that Kim presided over," the newspaper quoted the source as saying.
"He was arrested on-site and intensively questioned by the State Security Ministry," the paper claimed. "He was executed after other charges, such as corruption, were found during the probe."