JOHANNESBURG — South Africa’s main opposition party urged the government Wednesday to reveal who approved medical parole for a former police chief convicted of corruption charges.

The Democratic Alliance said “it is essential that the government comes entirely clean about how the decision . . . was made’’ on releasing Jackie Selebi. The release has led to a public outcry against what many call favoritism on part of the governing party.

Selebi was sentenced to 15 years in prison on corruption charges in 2010, with prosecutors saying he went on shopping sprees with drug dealers in exchange for sharing police information with them.

Officials say the 62-year-old is suffering from kidney failure, diabetes, and suspected cancer, and he was granted parole on health grounds Friday.

In a country ripe with corruption, granting medical parole is a contested issue often leading to accusations of favoritism on the part of the governing ANC party and President ­Jacob Zuma.