The office of South Korean President Park Geun-hye has confirmed revelations by an opposition legislator that it purchased about 360 Viagra pills and the generic version of the drug in December.

While the report has created a frenzy on the internet, Ms Park's office said the pills were bought to potentially treat altitude sickness for presidential aides and employees on Ms Park's May trips to Ethiopia, Uganda and Kenya, whose capitals are 1 to 2 kilometres (0.6 to 1.2 miles) above sea level.

The pills weren't used, said Jung Youn-kuk, a Blue House spokesman. South Korean doctors sometimes prescribe Viagra-style drugs to climbers because they are believed to be effective in preventing altitude sickness.

The presidential office also purchased a variety of injection drugs used for fatigue and anti-aging treatment, according to the office of legislator Kim Sanghee. Ms Park's spokesman explained that the presidential office purchases drugs for the president's entire staff including security officers.

The Viagra revelation is the latest twist in a massive political scandal building around Ms Park.

The president is bracing for an impeachment push by opposition parties and some members of her own Saenuri Party amid allegations that she let a confidante manipulate government affairs and amass an illicit fortune, a scandal critics say undermines the country's democracy.

On Sunday, prosecutors said they believe Ms Park was involved in the criminal activities of her longtime friend, Choi Soon-sil, and two presidential aides who allegedly bullied companies into giving tens of millions of dollars to foundations and businesses that Ms Choi controlled, and that she also enabled Ms Choi to interfere in state affairs. Prosecutors have indicted Ms Choi and the two former presidential aides.

Ms Park's office has denied the accusations and refused multiple attempts by prosecutors to interrogate her in person, although saying she will oblige to an independent probe by a special prosecutor.

The Seoul Central District Prosecutors' Office said investigators were sent to an office on Wednesday used by the senior presidential secretary for civil affairs to secure documents and other evidence. The search is apparently aimed at Woo Byung-woo, Park's former civil affairs secretary, who has been accused of failing to prevent Ms Choi from influencing state affairs and has been embroiled in separate corruption allegations surrounding his family.