North Korea has executed a vice premier for showing disrespect during a meeting presided over by leader Kim Jong-Un, and banished two other officials for re-education, South Korea said Wednesday.

Since taking power after his father's death in late 2011, Kim is believed to have executed or demoted a number of senior figures in what analysts say is an attempt to tighten his grip on power.

"Vice premier for education Kim Yong-Jin was executed," Seoul's Unification Ministry spokesman Jeong Joon-Hee said at a regular briefing.

Kim was killed by a firing squad in July as "an anti-party, anti-revolutionary agitator," added an official at the ministry, who declined to be named.

North Korean leader Kim Jong Un (C) attends the Fourth Session of the 13th Supreme People's Assembly (SPA) of North Korea in this undated photo released by North Korea's Korean Central News Agency (KCNA) in Pyongyang June 30, 2016. Photo: AFP

"Kim Yong-Jin was denounced for his bad sitting posture when he was sitting below the rostrum" during a session of North Korea's parliament, and then underwent an interrogation that revealed his other crimes, the official told reporters.

The mass-selling JoongAng Ilbo first reported on Tuesday that top figures had been punished, but identified the education official by a different name.

"He incurred the wrath of Kim after he dozed off during a meeting presided over by Kim. He was arrested on site and intensively questioned by the state security ministry," it quoted a source as saying.

 Fall of spymaster 

The unification ministry said two other senior figures were forced to undergo re-education sessions.

One of them was Kim Yong-Chol, a top official in charge of inter-Korean affairs and espionage activities against the South.

The 71-year-old Kim is a career military intelligence official who is believed to be the mastermind behind the North's frequent cyberattacks against Seoul.

Kim is also blamed by the South for the sinking of a South Korean warship in 2010 near the disputed sea border with the North in the Yellow Sea.

Kim was banished to an agricultural farm in July for a month for his "arrogance" and "abuse of power," the ministry official said.

Kim Yong-Chol, who was subsequently reinstated this month, is likely to be tempted to prove his loyalty by committing provocative acts against the South, the official said.

"Therefore, we are keeping a close tab on the North", he said.

South Korea's Yonhap news agency put the number of party officials executed during Kim Jong-Un's rule at over 100.

For the first time, Washington has blacklisted Kim Jong-Un and 10 other top North Korean officials for human rights abuses. Photo: AFP

The most notorious case was that of Kim's uncle and onetime No. 2 Jang Song-Thaek, who was executed for charges including treason and corruption in December 2013.

In April 2015, it was reported that Kim had his defence minister Hyon Yong-Chol summarily executed with an anti-aircraft gun.

Reports of the latest execution coincide with a series of high-profile defections from the North.

North Korea's deputy ambassador to Britain has defected to the South with his family, the unification ministry said earlier this month.

Thae Yong-Ho was driven by "disgust for the North Korean regime" and concerns for his family's future, it said.

Twelve waitresses and their manager who had been working at a North Korea-themed restaurant in China also made headlines when they arrived in the South in April as the largest group defection for years.

About 10 North Korean diplomats made it to the South in the first half of this year alone, Yonhap said, quoting informed sources.