Former President Nicolas Sarkozy's prison sentence has deepened divisions in France over judges' handling of political wrongdoing, months before far-right chief Marine Le Pen attempts to overturn an embezzlement conviction and run for top office.

The judge, Nathalie Gavarino, has received death threats and Paris prosecutors have opened two investigations into the matter.

Former French President Nicolas Sarkozy has been handed a five-year prison sentence for criminal conspiracy tied to illegal campaign financing from Libya, becoming the first post-war president to face imprisonment.