SEOUL (Reuters) - 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.

FILE PHOTO: The logo of SK Innovation is seen in front of its headquarters in Seoul, South Korea, February 3, 2017. REUTERS/Kim Hong-Ji/File Photo

The Constitutional Court dismissed Park on Friday last week 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 non-profit foundations backing the president’s initiatives.

Both denied wrongdoing.

The Samsung Group [SAGR.UL], 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 and Samsung denies wrongdoing.

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.

PRIVATE MEETINGS

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 memory-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.

The political turmoil comes at a time of rising tension with North Korea over its nuclear and missile programs, and with China over the deployment of a U.S. anti-missile system in South Korea that China sees as a threat to its security.

U.S. Secretary of State Rex Tillerson will visit South Korea, as well as Japan and China, this week.

The scandal has undermined support for the ruling conservatives and bolstered the chances of a prominent liberal, Moon Jae-in, who is leading in opinion polls.

The prospect of an opposition election victory has raised questions about the future in South Korea of the U.S.-made Terminal High Altitude Area Defense (THAAD) anti-missile system, which China opposes because it says its radar can penetrate its territory.

Tillerson will meet Prime Minister Hwang Kyo-ahn, who has been acting president since the impeachment vote, and Foreign Minister Yun Byung-se in Seoul on Friday.

He is not scheduled to see opposition figures, a U.S. State Department official said, raising questions about the durability of any agreements.

The aircraft carrier the USS Carl Vinson is in South Korean waters this week for exercises with South Korean forces.