Kim Jong-un aunt
Kim Kyong-hui, the sister of Kim Jong-il, is seen at left. Kim Jong-un (front row, 2nd R), youngest son of North Korea's leader Kim Jong-il, claps during a meeting of the ruling Workers' Party in Pyongyang September 28, 2010, in this video released on September 30, 2010.Reuters

North Korea's supreme leader Kim Jong-un had his aunt poisoned after she "argued" with him over her husband's execution, a defector has revealed. 

Kim Kyong Hui, the sister of Kim's father Kim Jong Il, was poisoned and killed in May last year, the defector, a senior North Korean official, told CNN

There has been intense speculation over the fate of Kim Kyong Hui, the widow of Jang Song Thaek - who was regarded as the second most powerful person in the country and was executed in December 2013 on charges of treason.

"On May 5th or 6th of last year....Kim Jong Un ordered his aunt, Kim Kyong Hui to be killed. Only his bodyguard unit, Unit 974, knew this -- now senior officials also know she was poisoned," the defector has now revealed. 

The once-powerful aunt's absence from public view for long had led to speculations last year that she was ill or may have died mysteriously.

Many reports suggested that she had died from a stroke while heatedly arguing with Kim over the phone about her husband's death. 

However, earlier this year, South Korea's National Intelligence Service (NIS) had reportedly claimed that Kim's aunt was still alive. 

The defector also said that Kim's uncle Jang was executed in an "underground secret room" and many of his aides were killed by a firing squad that used machine guns.

The defector's claim of Kim poisoning his aunt comes just days after a North Korean official had called reports that the ruler had ordered executions of 15 officials "malicious slander".