Prosecutors on Tuesday demanded a harsher punishment for the heir to the Samsung empire, appealing against a court ruling that sentenced him to five years in prison for bribery.

Lee Jae-Yong, the de-facto head of Samsung Electronics, was found guilty last week of bribery, perjury and other charges related to payments made by Samsung to ousted president Park Geun-Hye's secret confidante Choi Soon-Sil.

Four other top Samsung executives were also convicted, with two jailed for up to four years, and the other pair given suspended terms.

The prosecutors appealed part of the verdict that found Lee innocent of some of the bribery charges and said the punishment meted out to the five accused was too mild, Yonhap news agency said.

"In light of the roles the five accused played in the crime, which was the most outstanding among all wrongdoings committed by Park and Choi... the lower court ruling was too lenient", the prosecutors were quoted as saying in the appeal.

A day earlier, lawyers for Lee filed their own appeal against the conviction, claiming he is innocent of all charges.

In total 8.9 billion won ($7.9 million) was paid in bribes in return for favours including government support for Lee's hereditary succession at the group after his father was left bedridden by a heart attack in 2014, the court found.

Samsung is by far the biggest of the chaebols, as the family-controlled conglomerates that dominate Asia's fourth-largest economy are known, with its revenues equivalent to around a fifth of the country's GDP.

But while the economy is still growing, frustrations have mounted over inequality and the demonstrators who mounted giant candlelit protests against Park last year also targeted Lee and other chaebol chiefs.