Update: Tim Shorrock informs me “the extreme right-wing and highly unreliable chosun ilbo. no independent verification whatsoever,” so apologies for getting that wrong.
“Citing South Korean government officials, it said the gun battle erupted when vice marshal Choe Ryong Hae, director of the People’s Army General Political Bureau, tried to detain Mr Ri while carrying out North Korean leader Kim Jong-un’s order to sack him.”