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."
The second official was named as Hwang Min, of the Agriculture Ministry, who was executed "because policy proposals he had pushed for were seen as a direct challenge to the leadership of Kim Jong Un," the newspaper reported.
Details of those policies were not provided, although it has been confirmed that Hwang was replaced in a meeting of the North Korean parliament in late June.
The executions were carried out with anti-aircraft guns at a military academy in Pyongyang.
Using such weapons against anyone who crosses the regime has been reported in the past, notably in April 2015, when satellite images caught an imminent execution at a military training area outside Pyongyang.
There have also been reports of the Kim clan, which has ruled North Korea with an iron fist since 1945, using flame throwers and mortars to eliminate its opponents, although it is difficult to confirm all such claims.
The JoongAng Ilbo suggested the latest executions "may be interpreted as a new reign of terror in North Korea, prompted by a series of defections by senior officials that has rekindled talk of instability and disunity among the North Korea elite".
The most serious loss to Kim's regime was of Thae Yong Ho, deputy head of the North Korean Embassy in London, who arrived in Seoul with his wife and three children after fleeing the embassy in July.
There are additional reports that at least seven North Korean diplomats have fled overseas missions this year alone, including the third secretary at the embassy in Moscow.