A powerful uncle of North Korean leader Kim Jong-un has been removed from his post, South Korean media reports say.
Citing South Korea's intelligence agency, they say Chang Song-thaek, 67, lost his position as vice-chairman of the North's top military body.
Two close aides were also executed for corruption, according to the reports.
If confirmed, Mr Chang's removal would be the biggest upheaval in North Korea's leadership since Mr Kim succeeded his father, analysts say.
Kim Jong-un took over after Kim Jong-il died in 2011.
The latest reports emerged from an intelligence briefing given to South Korean lawmakers.
The National Intelligence Service (NIS) made the assessment based on information provided by multiple sources, the South's Yonhap news agency said.
It also quoted the intelligence service as saying two of Mr Chang's closest associates had been executed in public in late November.
Power behind the throne
The BBC's Lucy Williamson in Seoul says the reports are difficult to verify, and South Korea's spy agency has been proven wrong before. But if true, the development would mark a significant shift, she adds.
Mr Chang, who is married to Kim Jong-il's sister, was seen by some observers as the power behind the throne.
He climbed through the ranks of the secretive leadership of North Korea's Korean Workers Party (KWP) in the 1970s. In 1992, he was elected to its Central Committee.
However he has been targeted by purges in the past. In 2004, despite his place in the Kim family, he disappeared from public view.
One report at the time, citing South Korean intelligence, said Mr Chang had been placed under house arrest. Others suggested he had been sent for "re-education".
However, two years later he appears to have been reinstated. He was regarded as an economic reformer and a major influence on Kim Jong-un.
He held key positions in both the Communist Party and the National Defence Commission.
Apart from chronic economic problem, North Korea is involved in a protracted stand-off with its neighbours and Western powers over its nuclear weapons programme.
Tensions between the two Koreas rose after the North's third nuclear test in February.
Angered by expanded UN sanctions and annual US-South Korea military drills, Pyongyang threatened attacks on Japanese, South Korean and US military targets in the region.