Seoul - South Korean prosecutors said on Sunday that President Park Geun-Hye colluded with her close confidante in a corruption and influence-peddling scandal that has sparked massive nationwide protests and calls for her impeachment.Park's long time friend Choi Soon-Sil was charged on Sunday with coercion and abuse of power, as was one of the president's former aides.Another presidential aide was charged with leaking confidential state documents."The president played a collusive role in a considerable portion of the criminal activities involving the (three) people," said Lee Young-Ryeol, a Seoul prosecutor who is leading a probe into the scandal.Choi, 60, has been accused of using her personal ties to Park to meddle in state affairs and of coercing local firms to "donate" more than $60 million to dubious non-profit foundations. She allegedly then used some of the funds for personal gain.Park faces allegations that she helped Choi extract money from the firms and that she ordered her aides to leak state documents to Choi, who has no official title or security clearance.'Unfair political attacks'Under the constitution a sitting president cannot be charged with a criminal offence except insurrection or treason. But she can still be probed by prosecutors and possibly charged after leaving office.Lee acknowledged that prosecutors could not formally charge Park at present but vowed to continue to investigate her.Prosecutors had previously described the conservative leader as a witness to Choi's crimes but changed her status to that of a criminal suspect, said a senior prosecutor at the investigative team."From now on, she will be probed as a suspect... for violation of Section 30 of the criminal code on collusion," Roh Seung-Kwon told reporters.Park's spokesperson Jung Youn-Kuk angrily rejected the prosecutors' accusations, describing them as "unfair political attacks" based on "imagination and guesswork".Park had earlier promised to answer prosecutors' questions "sincerely" - a move which would make her the first South Korean president to be quizzed by prosecutors while in office.But her lawyer Yoo Young-Ha said on Sunday Park would not meet prosecutors and would only deal with an independent team of investigators which will soon take over the probe.Impeachment calls The latest revelations piled pressure on opposition party lawmakers to seek the impeachment of Park, the daughter of a former president, who has about a year left in her five-year term.The main opposition Democratic Party has not seriously pushed for Park's impeachment due to fears of a backlash from conservative voters before the presidential election in 2017.But recent opinion polls suggest growing support for impeachment, with the latest survey showing 74% backing.A growing number of opposition lawmakers are urging their party leaders to seek impeachment, and about 30 members of Park's own ruling party also voiced support for the move.More than 50 local firms including Samsung and Hyundai were forced to donate a total of 77.4 billion won ($65.5 million) to the two foundations controlled by Choi.Many made the donations due to fear of reprisals such as harsh tax audits or difficulties getting regulatory approvals for their businesses, prosecutor Lee said.Choi also pressured major firms including the South's largest carmaker Hyundai and top steelmaker Posco to award lucrative contracts to firms linked to her, he added.