Former Israeli Prime Minister Ehud Olmert leaves Tel Aviv District Court, in this May 13, 2014 file picture.[Photo/Agencies]

JERUSALEM -- Former Israeli Prime Minister Ehud Olmert will serve 18 months in prison after the Supreme Court partially accepted his appeal against a district court decision on a six-year imprisonment over bribery charges on Tuesday.

An extended panel of five judges in the Jerusalem Supreme Court accepted several clauses of Olmert's appeal and rejected others, and decided to decrease his prison sentence from six years to one and half years in prison.

Ehud Olmert, who served as prime minister between 2006 and 2009, was sentenced to six years in prison in May 2014 by the Tel Aviv District Court magistrate for graft charges committed during the time he served as mayor of Jerusalem between 1993 and 2003.

The corruption affair involves the development of the Holyland residential complex in Jerusalem. Olmert had allegedly received around 560,000 shekels (around 144,000 U.S. dollars) in bribes from contractors in order to push the project forward. Ten other officials and contractors were also convicted in the affair.

He is the first former prime minister to be convicted of bribery and sentenced to prison.

Judge David Rozen, who sentenced him to prison last year, wrote that a person at such a senior position who accepts bribery "is like a traitor to his people" as he had "used his elevated positions to make money or for personal gain."

In May of this year, Olmert was sentenced to eight months in prison in a different affair, came to be known as the "Money Envelopes" affair, by the Jerusalem District Court.

In this affair, Olmert was found guilty of fraud, breach of trust and aggravated fraud, for receiving cash-filled envelopes from American businessman Morris Talansky. Olmert appealed this sentence as well.

Olmert, originally a member of the Likud party who joined the center-left Kadima party in 2005, resigned from his post as prime minister in 2008, once corruption allegations started to surface against him.