Chinese authorities have seized assets worth at least 90 billion yuan ($14.5 billion) from family members and associates of retired domestic security tsar Zhou Yongkang.
More than 300 of Zhou's relatives, political allies, proteges and staff have also been taken into custody or questioned in the past four months, the sources, who have been briefed on the investigation, told Reuters.
Zhou has been under virtual house arrest since authorities began formally investigating him late last year, said Reuters. He is the most senior Chinese politician to be ensnared in a corruption investigation since the Communist Party swept to power in 1949.
Xi ordered a task force formed in late November or early December to look into accusations against Zhou, said Reuters. They have not said what the allegations were except that they were related to violating party discipline, official jargon for corruption.
A third source with ties to the leadership said Zhou had refused to cooperate with investigators, insisting he was the victim of a power struggle.
Zhou rose through the ranks of China's oil and gas sector before joining the elite Politburo Standing Committee in 2007, where as domestic security chief his budget exceeded defense spending. He retired in 2012 and was last seen at an alumni event at the China University of Petroleum on October 1, Reuters said.
Investigators have also confiscated about 300 apartments and villas worth around 1.7 billion yuan, antiques and contemporary paintings with a market value of 1 billion yuan and more than 60 vehicles, Reuters said. Other items seized included expensive liquor, gold, silver and cash in local and foreign currencies.