South Korea's special prosecutor's office said on Wednesday it had expanded charges against Samsung Group chief Jay Y. Lee to include hiding the proceeds of a criminal act before it decided to seek a warrant for his arrest for a second time.

Lee, the third-generation leader of South Korea's top conglomerate, has been identified as a suspect by prosecutors in an influence-peddling scandal that could topple President Park Geun-hye. He was questioned for more than 15 hours straight this week, his second marathon grilling in a month.

The decision to add extra charges, which included hiding assets overseas, was made after a Seoul court denied prosecutors' first attempt to secure an arrest warrant for Lee last month, a spokesman for the special prosecutor's office said.

"For three weeks, we secured additional evidence that we can be sure about, and after careful deliberation have requested (an arrest warrant) for the second time," spokesman Lee Kyu-chul told reporters without elaborating.

South Korea's special prosecutor has focused on Samsung Group's relationship with Park, accusing Lee in his capacity as Samsung chief of pledging 43 billion won ($37.7 million) to a business and organisations backed by Park's friend, Choi Soon-sil, in exchange for support of a 2015 merger of two Samsung companies.

Park, Choi, and Samsung Group have denied bribery accusations.

Park was impeached by parliament in December and South Korea's Constitutional Court will decide whether to uphold that decision. She has been stripped of her powers in the meantime.

The prosecution is also bringing an additional charge of perjury against Lee.

They have also requested an arrest warrant for Samsung Electronics Co Ltd President Park Sang-jin, who was also questioned on Monday. The charges he and Lee face also include bribery and embezzlement.

A Seoul court said on Tuesday it would hold a hearing on the request for arrest warrants at 10:30 a.m. (0130 GMT) on Thursday. Based on previous instances, the court's decision is expected late on Thursday or most likely early Friday.

The prosecution also said it would decide later whether to seek charges against three other Samsung executives. Samsung Group President Chang Choon-ki was also questioned on Sunday and another executive on Monday.

On Wednesday, Samsung Group repeated an earlier denial on its official Twitter account: "Samsung has absolutely never bribed the president seeking something in return or sought illicit favours."

"We will do our best for the truth to be revealed in court," it said. 

Earlier this month, prosecutors searched the offices of the antitrust agency, the Korea Fair Trade Commission, and financial regulator, the Financial Services Commission, as part of their investigation of Samsung Group.

The special prosecution office's mandate to conduct the graft investigation will expire on February 28, unless it is extended.