The ruling Saenuri Party will Thursday launch an internal investigation into an alleged money-for-nomination scandal, an official said, as the embattled party seeks to minimize the scandal's fallout ahead of December's presidential election.

The probe comes as prosecutors have started their own investigation into allegations that Rep. Hyun Young-hee of the Saenuri Party won a proportional representation seat in April's general elections after paying 300 million won ($266,170) to Hyun Ki-hwan, then a member of the party's nomination committee.

The internal investigation also comes at the request of three of the party's five presidential contenders. The three -- Yim Tae-hee, a former chief of staff to President Lee Myung-bak; Gyeonggi Province Governor Kim Moon-soo; and former South Gyeongsang Province Governor Kim Tae-ho -- boycotted the primary race last Friday after calling on party Chairman Hwang Woo-yea to take responsibility for the scandal. They returned to the race two days later on the condition that Hwang would step down if the prosecution finds the allegations to be true and that the party would form a truth-finding committee.

"We will receive recommendations for committee members today from the presidential candidates and then seek the Supreme Council's approval on Thursday," Rep. Suh Byung-soo, the party's secretary general, told Yonhap News Agency in a phone call. "We plan to form a committee of around 10 people and appoint a neutral figure from outside (the party) as chairman."

Under Sunday's agreement, all five presidential candidates will recommend one person each, while the remaining seats will be filled by neutral figures and those recommended by the party's leadership.

Kim Moon-soo and Kim Tae-ho have recommended a lawmaker and a lawyer, respectively, while the other candidates, including the party's presidential frontrunner Park Geun-hye and former Incheon Mayor Ahn Sang-soo, have yet to finalize their recommendations.

Apparently mindful of the damage the scandal could cause to Park's presidential chances, the Saenuri Party's ethics committee decided Monday to expel both Hyuns from the party.

Rep. Hyun's expulsion will be subject to approval by at least two-thirds of the party's 149 lawmakers at a general meeting, while the fate of the former nomination committee member will be determined at a meeting of the party's Supreme Council.

If expelled, the two Hyuns will be banned from returning to the party for the next five years. Rep. Hyun will, however, be able to keep her legislative seat as an independent.

Both the lawmaker and the former nomination committee member have flatly denied the accusations. Despite a shared last name, the two are not related.

Emerging early Tuesday morning from 14 hours of intensive questioning by prosecutors at the Busan District Prosecutors' Office, Rep. Hyun told reporters that she had "sincerely responded (to the questions) and the truth will soon be uncovered."

The lawmaker has been based in the southeastern city of Busan for most of her career and previously served as a member of the local city council, most recently in 2006-2008.

Hyun Ki-hwan and other key suspects in the scandal have also undergone questioning by prosecutors.

Meanwhile, the main opposition Democratic United Party (DUP) has stepped up its offensive against the rival party, urging Park to take responsibility by withdrawing from the presidential race and giving up her own proportional representation seat in parliament.

The scandal has been especially painful for the Saenuri Party as it won April's parliamentary elections on the back of sweeping reforms, including what it said was a more fair and transparent nomination system. Park was party chief at the time.

Some DUP lawmakers accused the prosecution of trying to cover up the case.

"The prosecution should not focus on minor issues and simply determine whether (the money) was given or not, but investigate every detail of the structural problems within the Saenuri Party's (former) nomination committee," Rep. Park Beom-kye of the DUP said during a meeting with fellow party lawmakers. (Yonhap)