SEOUL - Prosecutors questioned three officials linked to South Korea's third-largest conglomerate, SK Group, on Thursday as part of a widening corruption scandal that led to the dismissal of President Park Geun-hye.

The Constitutional Court dismissed Park on Friday when it upheld a December parliamentary impeachment vote.

An election for a successor will be held on May 9.

Park, South Korea's first democratically elected president to be removed from office, has been accused of colluding with a friend, Choi Soon-sil, to pressure big businesses to contribute to nonprofit foundations backing the president's initiatives.

Both denied wrongdoing.

The Samsung Group, South Korea's largest conglomerate, is already embroiled in the scandal and its head, Jay Y. Lee, is in jail on trial on bribery, embezzlement and other charges.

Lee denies all charges.

A spokesman for the Lotte Group said on Wednesday it was cooperating with the prosecutors' investigation.

The three officials linked to the SK group include Kim Chang-geun, the former chairman of the semiconductor-to-telecom group's top decision-making committee, an SK Group spokesman confirmed.

"We will actively straighten out suspicions that are different from facts," the spokesman said.

Park has been summoned for questioning next Tuesday.

Kim had a private meeting with Park in July 2015, around the time Park was holding a series of meetings with heads of conglomerates, the Yonhap news agency reported.

The SK Group controls companies such as the world's second-biggest chip maker, SK Hynix Inc, and South Korea's biggest telecoms company, SK Telecom.

Prosecutors have not said how long they think their investigation would last.