North Korean dictator Kim Jong-un has had a senior official executed because he did not sit properly in a meeting.

Education minister Kim Yong-Jin, 63, was shot by a firing squad after his "bad sitting posture" in parliament incurred the wrath of the 32-year-old tyrant.

The slouching vice premier was interrogated and found to be an "anti-revolutionary agitator" before his execution in July, a South Korean official said.

"Vice premier for education Kim Yong-Jin was executed," unification ministry spokesman Jeong Joon-hee said.

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"Kim Yong-Jin was denounced for his bad sitting posture when he was sitting below the rostrum," he added, referring to North Korea's parliament.

Kim Jong-un was in the government meeting and was infuriated after Kim Yong-Jin sat in his chair "with a bad attitude". Another South Korean official said the minister's poor posture was spotted at a meeting on June 29.

"He was later accused of being anti-revolutionary following a probe and a firing squad execution was carried out in July," the official told South Korean newspaper JoongAng Daily.

Two other senior North Korean officials were also banished to "ideological re-education" farms.

Last year it was reported defence minister Hyon Yong-chol was executed by anti-aircraft gun. But the new report corrects claims made in the South Korean media that two other North Korean officials met a similar fate.

Kim Jong-un's regime is especially paranoid in recent weeks after a senior official at the London embassy defected to South Korea with his family.

North Korea rarely announces purges or executions, although state media confirmed the killing of the tyrant's uncle Jang Song Thaek in 2012 for "crimes damaging to the economy".

A former defence minister, Hyun Yong Chol, is also believed to have been executed last year for treason, according to the South's spy agency.