By Se Young Lee and Ju-min Park

SEOUL (Reuters) - Samsung Group [SAGR.UL] leader Jay Y. Lee arrived at the South Korean special prosecutor's office on Thursday for questioning over bribery suspicions as part of a widening influence-peddling scandal that may permanently unseat President Park Geun-hye.

The prosecution named Lee as a suspect on Wednesday and is investigating whether 30 billion won ($25.28 million) provided by Samsung to a business and foundations backed by Park's friend, Choi Soon-sil, were connected to a 2015 decision by the country's national pension fund to support a controversial merger of two group affiliates.

"I am very sorry to the South Korean people for not showing a better side," Lee told reporters after arriving at the office in a black Korean-made Ssangyong sedan, greeted by protesters holding signs calling for his arrest and accusing him of being an accomplice to President Park.

Wearing a dark suit, white shirt and dark red necktie, Lee bowed after making his brief remarks to a crowd of journalists.

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. The impeachment must be upheld or overturned by the Constitutional Court.

The scandal has triggered big weekly rallies calling for Park to step down. Park has denied any wrongdoing, but has apologized.Choi, 60, who has known Park for four decades, is accused of colluding with Park to pressure big businesses, including Samsung Group, to contribute to non-profit foundations backing the president's initiatives.

Choi, in jail since late October, is currently on trial charged with abuse of power, attempted fraud and bribery. She has plead not guilty

Proving quid-pro-quo dealings between the Choi-linked organizations and Samsung are critical to prosecution efforts to bolster its case against the Korean president and show that she, or a surrogate such as Choi, collected bribes in exchange for favors, analysts said.

A special prosecution spokesman on Wednesday did not comment on whether Jay Y. Lee or other Samsung executives will be indicted but would not rule out the possibility of the prosecution seeking an arrest warrant against Lee.

The 48-year-old Lee took over as leader of the country's biggest conglomerate after his father, founding family patriarch Lee Kun-hee, was incapacitated by a May 2014 heart attack.

(Reporting by Se Young Lee and Ju-min Park; Editing by Michael Perry and Tony Munroe)