A close friend of the former South Korean president, Park Geun-hye, has been sentenced to 20 years in prison over corruption, in a case that led to Park's impeachment.

Choi Soon-sil was found guilty on Tuesday by the Seoul Central District Court of using her friendship with Park to meddle in state affairs for personal gain.

She was convicted of bribing South Korean conglomerates including Samsung, in a scandal that triggered chaos among the country's political and business elite.

The 61-year-old, who was detained in November 2016, was also fined $16.6m.

Choi is the confidante of Park, who was dismissed from the presidency last year after being impeached over a corruption scandal that paralysed her administration and triggered massive street protests. Park denies any wrongdoing.

Prosecutors had demanded a 25-year sentence for Choi.

Al Jazeera's Natasha Ghoneim, reporting from the South Korean capital, said: "Prosecutors described Choi as a woman who shook South Korean society's foundation and paralysed the political process to the extent that this will impact generations to come."

"Choi has said all along that this was political revenge, she is innocent and that she believes due to the bias against her she was not going to be able to get a fair trial," Ghoneim added.

Earlier this month, an appeals court freed Samsung Group heir Lee Jae-yong and reduced his five-year jail term, as it dismissed a number of charges against him.

The billionaire was convicted in August last year of bribing Park with $8.2m in return for government backing of a business merger.

Amid the bribery claims, thousands protested calling for Park to step down.

She was indicted on multiple charges, including bribery, a month after she was fired as president by the top court in March.

A verdict in her case is expected in the next couple of months.

Liberal politician Moon Jae-in was elected the new president in May.