SEOUL, Nov. 7 (Xinhua) -- South Korean prosecutors launched an investigation on Monday into President Park Geun-hye's closed-door meeting with heads of major conglomerates last year for Park's possible role in helping raise funds for two foundations presumably controlled by her long-time confidante Choi Soon-sil.

The prosecution's special investigative unit in charge of probe into the Choi Soon-sil case questioned two senior officials of the Federation of Korean Industries (FKI), a domestic lobby group for conglomerates, according to local media reports. The officials were grilled over the meetings that were held for two days last July.

On July 24 last year, President Park held an open lunch meeting with 17 chiefs of major conglomerates in the presidential office, asking the participants to support the establishment of non-profit foundations for the purpose of boosting the popularity of so-called Korean Wave.

After the opening event, Park allegedly held closed-door meetings with seven of the participants, separately one by one, that continued through the next day. Among the participants were Samsung Electronics Vice Chairman Lee Jae-yong, Hyundai Motor Group Chairman Chung Mong-koo and LG Group Chairman Ku Bon-moo.

Prosecutors reportedly found a circumstantial evidence that President Park probably ordered the seven chaebol chiefs to make donations to the Mir and K-Sports foundations, or cultural and sports funds presumably controlled by Choi.

The findings were based on an investigation into Ahn Jong-beom, former senior presidential secretary on policy coordination, who has been placed under a formal custody for alleged charges of helping Choi pressure big corporations into donating tens of millions of U.S. dollars to the dubious foundations.

The prosecution reportedly plans to summon officials close to the conglomerate chiefs, who attended the closed-door meetings, for questioning if the ongoing probe requires it.

The mobile phone of Jeong Ho-seong, former presidential secretary who had assisted Park for two decades, is being analyzed by prosecutors. Jeong, who has been formally detained, is charged with bringing confidential presidential documents to Choi on a daily basis.

Choi, the president's decades-long confidante, is suspected of meddling in state affairs behind the scenes. Allegations include her intervention in the appointment of ministers and illicit review and recommendations on diplomatic, defense and economic affairs though she has no security clearance and public position.

Public attention is centered on whether prosecutors will investigate President Park as the first South Korean female leader said last Friday that she would accept an investigation into herself "if necessary."

Park made her second public apology last week but failed to appease the public anger as about 200,000 South Koreans rallied in central Seoul at the weekend to demand Park's resignation. Some 100,000 attended separate rallies held in major cities nationwide.

Approval rating for Park was 11.5 percent last week, down 7.5 percentage points from the previous week, according to a Realmeter poll of 2,528 adults conducted from Monday to Friday.

The number was the lowest for any South Korean president, keeping a downward trend for five weeks in a row. According to a Gallup Korea survey released on Friday, Park's support scores dropped to 5 percent, lower than any of her predecessors.

Traditional support base for Park rapidly alienated from the embattled president, with an approval rating in the North Gyeongsang province tumbling 20.1 percentage points compared with a week ago, the Realmeter survey showed. The province is regarded as a political home turf for Park and the ruling Saenuri Party.

Calls mounted in the opposition bloc for President Park's retraction of prime minister nomination, while the ruling Saenuri Party demanded she leave her party.

Choo Mi-ae, chairwoman of the main opposition Minjoo Party, told a supreme council meeting that Park must cancel the cabinet reshuffle, which goes against the public sentiment, and nominate a new prime minister proposed by the parliament.

President Park appointed three cabinet members, including the prime minister nominee Kim Byong-joon, last week, but the oppositions have boycotted parliamentary hearing for approval as the nomination was a result of "unilateral" decision by the president without any consultation with the parliament.

Meanwhile, former Saenuri Party chairman Kim Moo-sung held an emergency press conference, saying President Park must drop her party affiliation with a sense of responsibility to save the party.

Kim is seen as one of key men in the non-President Park faction within the ruling party.