An unnamed South Korean official was cited by the Yonhap news agency as saying Kim Jong Gak was removed from his post as the top minister of the People's Armed Forces. He was apparently replaced by Kim Kyok Shik, a general believed to have ordered the sinking of a South Korean warship last year.
Last week, anonymous officials in Seoul said the North Korean government was testing the loyalty of top figures in the administration of Kim Jong Un, who took over the country after the December death of his father, Kim Jong Il.
A series of shake-ups occurred recently among members of North Korea's top military brass.
North Korea is suspected of carrying out work at military installations that could be a sign that Pyongyang is prepared to launch a new missile. Similar launches in 2006 and 2009 coincided with North Korean nuclear tests.
Yonhap reports that U.S. and South Korean diplomats may be moving to resume stalled nuclear negotiations, meanwhile. It reported a U.S. official may have visited Pyongyang in August to discourage the North Koreans from making any provocative moves ahead of U.S. elections.
The reporting agency adds that South Korea, for its part, was forced to scrub a rocket launch to deploy a satellite after problems were reported with its second stage thrust system.