Image copyright Reuters Image caption Ms Park has seen her approval ratings plummet amid the scandal South Korean authorities have raided the offices of Samsung and the national pension fund as part of a corruption investigation linked to the president.
They are probing whether Park Geun-hye pressured the fund to support a Samsung merger, said the Yonhap news agency.
In return, Samsung is alleged to have given financial favours to Ms Park’s confidante Choi Soon-sil, Yonhap said.
The scandal has led to growing calls for Ms Park’s resignation, but she has said the allegations are “fantasy”.
Ms Choi, who has been charged with coercion and attempted fraud, is accused of using her close relationship with Ms Park to obtain favours and funds for her own gain.
Earlier this week prosecutors said Ms Park had a “considerable” role in the scandal.
The allegations have enraged the South Korean public, and caused Ms Park’s approval ratings to plummet. However, she has resisted the calls for her to resign and has yet to agree to be questioned by investigators.
Her spokesman rejected the prosecutors’ case as speculation built on “a house of fantasy”.Image copyright EPA Image caption South Koreans have staged demonstrations calling for Ms Park’s resignation
Samsung’s offices had already been raided over related allegations.
Wednesday’s raid had to do with a merger last year between the electronics giant’s construction arm, Samsung C&T, and an affiliate firm, Cheil Industries.
The deal went through despite significant opposition from shareholders, who said it would hurt minority shareholders while benefiting the family of Samsung’s group owner Lee Kun-hee.
South Korea’s National Pension Service (NPS), which owns stakes in both companies, sealed the deal by voting in favour of it.
Prosecutors allege that Samsung gave €2.8m euros ($3.1m;£2.5m) to a company co-owned by Ms Choi and her daughter, in return for Ms Park’s support for the deal.
Samsung was also among several conglomerates that gave millions of dollars to two non-profit foundations owned by Ms Choi, after the latter allegedly pressured them for donations.
Samsung and the pension fund confirmed the raids without giving further details.Image copyright AFP/Getty Images Image caption At the centre of the probe is Choi Soon-sil, a close confidante of Park Geun-hye
Ms Park is accused of giving Ms Choi inappropriate access to government policy-making and decisions.
She has since acknowledged that she committed lapses, and apologised twice on national television.
Separately on Wednesday, Ms Park’s office confirmed a report that they had bought hundreds of Viagra pills on behalf of the president.
A spokesman told reporters that the drug, better known for treating erectile dysfunction among men, was meant to help Ms Park and her staff cope with high-altitude sickness during trips to Africa.