German authorities have rejected a former Auschwitz death camp guard's bid for clemency, removing the final barrier to him serving his sentence for accessory to murder.

Lueneburg prosecutors' spokeswoman Wiebke Bethke said Wednesday her office had rejected former SS sergeant Oskar Groening's clemency request filed earlier this week. She said regulations prevented her from releasing any further details.

The 96-year-old was convicted in Lueneburg in' 2015 as an accessory to the murder of 300,000 Jews and sentenced to four years in prison. He hasn't yet spent any time behind bars because of the appeals process.

Germany's highest court rejected his last legal appeal in December.

Hannover prosecutors, who have been handling his case, are expected to soon summon him to begin serving his sentence.