South Korean prosecutors raided the offices of Samsung Group following media reports of alleged links with a confidante of President Park Geun-hye who has been indicted in an influence-peddling scandal, a prosecution official said.

Wednesday’s raid comes as Samsung faces allegations that it bribed Park’s confidante Choi Soon-Sil to win state approval for a controversial merger it sought last year.

Prosecutors also raided South Korea’s largest pension fund, the National Pension Service (NPS), a spokesperson said. The NPS oversees funds worth $461bn, making it the world’s third largest service of its kind.

The Yonhap news agency reported that investigators were probing NPS’s decision to approve the $8bn merger of Samsung C&T Corp and Cheil Industries last year.

The raids signalled that prosecutors are expanding their investigation into allegations of influence-peddling in the corruption scandal that has rocked Park’s presidency over the relationship between the government and big businesses.

NPS has come under scrutiny by the media and civic groups over its approval as a major shareholder of the merger between two affiliates of Samsung Group, South Korea’s largest family-run conglomerate.

Meanwhile, South Korean opposition parties said this week that they will review strategies to impeach Park.

“Based on the consensus that President Park is the centre of the abuse of power scandal, the best course of action to minimise the vacuum in government and to restore constitutional rule is for her to step down,” the leaders of three opposition parties said in a joint statement on Sunday.

Corruption allegations

Park and Choi Soon-sil are under investigation for allegedly improperly pressuring major conglomerates, including the Samsung Group, to raise funds for foundations that backed Park’s policy of promoting the cultural and sports communities.

The merger of the Samsung affiliates was approved by shareholders in July 2015 and prosecutors said the two foundations involved were set up in the next six months.

Park, whose five-year term ends in February 2018, has resisted calls to resign but has apologised twice, saying she only sought to benefit the economy and not herself, but acknowledges carelessness in her ties with Choi.

The president angrily denied the prosecutors’ accusations, calling them a “fantasy” based on “imagination and guesswork”.

READ MORE: Seoul rally urges Park Geun-hye to resign

“It’s an unprecedented move, a sitting South Korean president being questioned face-to-face in a criminal case,” said Al Jazeera’s Harry Fawcett, reporting from Seoul.

“It does, however, look unlikely that Park is going to accede to this demand.”

Park had earlier promised to answer questions “sincerely” but her lawyer said on Sunday that the president would not meet prosecutors and would only deal with an independent team of investigators that will soon take over the probe.

A key presidential aide who was once a star prosecutor and justice minister Kim Hyun-Woong both offered their resignations on Wednesday, as tensions between Park and prosecutors reached new heights.

Choi and the former presidential aide, An Chong-bum, were indicted on Sunday and charged with abuse of power, a major blow to the president’s fight for political survival.

Activists said a fifth weekly protest in Seoul on Saturday would draw between 1.5 million and two million people, which would make it the largest ever public demonstration in South Korea.