Prosecutors have been checking if Samsung's support for a business and foundations backed by Park's friend, Choi Soon-sil, was connected to a 2015 decision by the national pension service to back a controversial merger of two group affiliates.

Samsung has acknowledged making contributions to two foundations as well as a consulting firm linked to Choi. The prosecution summoned two senior Samsung Group officials this week for questioning, though they were classified as witnesses.

Lee, the vice chairman of flagship affiliate Samsung Electronics Co Ltd, has managed South Korea's top conglomerate after his father and founding patriarch Lee Kun-hee was incapacitated after a May 2014 heart attack.

At a December parliament hearing, the executive denied that the firm paid bribes to pave the way for the 2015 merger.

Lee Kyu-chul, a spokesman for the special prosecution team, told a briefing Lee had been summoned for questioning at 9:30 a.m. (0030 GMT) on Thursday, over suspicions including bribery, but did not elaborate.

"All possibilities are open," the spokesman replied, when asked if the prosecution team would request an arrest warrant for the Samsung Group leader.

A Samsung Group spokeswoman declined to comment.

President Park could become South Korea's first democratically elected leader to leave office early after parliament voted in December to impeach her over the corruption scandal, a decision that must be approved or overturned by the Constitutional Court.

(Reporting by Se Young Lee and Ju-min Park; Editing by Clarence Fernandez)