Ex-North Korean leader Kim Jong-il's former sushi chef believes it is "unbelievable and impossible" that current leader Kim Jong-un was behind the purge and execution of Jang Song-taek.

Kenji Fujimoto, who returned to Japan in 2011 after 13 years in the North, visited Pyongyang in July last year at the invitation of Kim Jong-un and was a guest at a banquet attended by Kim, his wife Ri Sol-ju and Kim's younger sister Yo-jong.

Also present were Jang and former ambassador to Switzerland Ri Su-yong, who is also rumored to have been executed.