Former French president Nicolas Sarkozy will have two police officers stationed in nearby cells while he is in prison to ensure he comes to no harm, France's interior minister said on Wednesday.

Sarkozy on Tuesday began a five-year sentence after being convicted of conspiring to raise campaign funds from Libya, arriving at La Sante prison in Paris - a stunning downfall for a man who led the country between 2007 and 2012.

Interior Minister Laurent Nunez told Europe 1 radio that two police officers who are part of the security detail protecting former presidents will be stationed permanently in neighbouring cells throughout Sarkozy's incarceration.

"The former president of the republic is entitled to protection because of his status. There is obviously a threat against him, and this protection is being maintained while he is in detention," Nunez said.

He added that the officers would remain at Sarkozy's side throughout his incarceration "as long as it is necessary". The officers will be members of a team doing rotating shifts in the prison, French media reported.

Sarkozy will be held in La Sante's isolation unit, where inmates are housed in single cells and kept apart during outdoor activities, meaning he should not be in contact with other inmates.

Prison guard unions protested over the presence of police inside the prison.

CGT union's Nicolas Peyrin said La Sante staff are perfectly able to ensure inmate safety and that police were not necessary.

"There is no added value," he told BFM television.

Hugo Vitry, a prison guard at La Sante and head of the local branch of the Force Ouvriere union, said guards had not been informed about Sarkozy's security detail.

"We have contacted the prison administration and the Ministry of Justice to demand explanations," he told BFM.

Sarkozy's lawyers have filed a request for early release, pending his appeals trial, and said that they expected this request to be reviewed in about a month. They said they hoped to get him freed on early release by Christmas.

Sarkozy has consistently denied wrongdoing and has called the case politically motivated.