(CNN) South Africa's justice minister on Wednesday ordered a review of Oscar Pistorius' pending parole, meaning the former Olympian probably won't be granted a transfer from prison to house arrest this week as had been expected.

Pistorius, who was sentenced in October to five years in prison for culpable homicide in the 2013 killing of his girlfriend Reeva Steenkamp , had been expected to be transferred to house arrest Friday at the recommendation of a parole board.

But Justice and Correctional Services Minister Michael Masutha, urged by a women's group to halt the transfer, ordered a review of that decision on the grounds that the parole ruling may have been made too early.

"We've accepted the decision by the Ministry of Justice and are considering our options," Anneliese Burgess, the Pistorius family spokeswoman, said in a statement.

Under South Africa's Correctional Services Act, Pistorius must serve at least one-sixth of his sentence -- in this case, 10 months -- "before being considered for placement" to house arrest.

Friday is 10 months to the day after Pistorius was sentenced, and the prison parole board, when it announced its decision in June, believed Pistorius would therefore be eligible to transfer at that moment.

But Masutha on Wednesday said that according to his reading of the law, the board shouldn't have even considered the transfer until the 10-month mark.

"It is apparent therefore that the decision to release him on 21 August 2015 was made prematurely on 5 June 2015 when the offender was not eligible to be considered at all," Masutha's office said in a statement.

Masutha said he is asking a parole review board to examine the first panel's decision. It wasn't immediately clear when that review would be completed.

Because of the review, it is unlikely that Pistorius will be released to house arrest Friday, Justice Ministry spokesman Mthunzi Mhaga said.

Stephan Terblanche, a sentencing expert and professor at University of South Africa, said parole boards frequently make decisions about inmates before the minimum sentence period has been completed.

He also said involvement by a South African justice and correctional services minister in such a case is not common.

"Certainly for a minister to get involved in an individual case is unusual," Terblanche said.

Masutha's office said he examined the parole case after the Progressive Women's Movement of South Africa sent him a petition. The group argued that it would be insensitive for authorities to transfer Pistorius in August, which is Women's Month in South Africa, the office said.

In a 2014 trial, a judge found Pistorius to be not guilty of murder, but guilty of culpable homicide in Steenkamp's death in his home on Valentine's Day 2013. In South Africa, culpable homicide means a person is judged to have killed someone unintentionally but unlawfully.

Pistorius, now 28, acknowledged firing shots through the bathroom door in his home but said he thought there was an intruder in the bathroom rather than his girlfriend.

Prosecutors are appealing the verdict, believing Pistorius should be convicted of murder. The state's appeal is set to take place in November.

Pistorius, whose legs were amputated before his first birthday, was famed for his track career. Running on prosthetic blades, he won gold medals at the 2004 and 2008 Paralympics before competing in the 2012 Summer Olympics in London, where he ran in the 400-meter race and the 4x400-meter relay.

Steenkamp, a model and law school graduate, would have turned 32 on Wednesday. Some of her relatives spent part of the day on a beach near Port Elizabeth, South Africa, throwing roses into the ocean in her honor, South African broadcaster eNCA reported.