Special prosecution spokesman Lee Kyu-chul said Lee has argued that he is a victim of coercion due to pressure from President Park Geun-hye but that the prosecution was not convinced of his argument.
The 48-year-old executive was named a suspect as part of an investigation into a graft scandal that has led to the impeachment of Park.
The spokesman also said Samsung Group Vice Chairman Choi Gee-sung had been classified as a suspect on suspicion of bribery but did not elaborate further.
(Reporting by Ju-min Park and Se Young Lee; Editing by Nick Macfie)