Croatia's constitutional court said Monday it had abolished a jail sentence against former prime minister Ivo Sanader in one of several corruption cases against him and ordered a retrial.

The court has concluded that Sanader's right to a fair trial had been violated and that the sentence was based on a tougher law than it should have been.

However, the court said it had not determined whether Sanader -- who was prime minister from 2003 to 2009 -- was guilty of the crime itself as it was not within its jurisdiction.

In June 2014, Croatia's Supreme Court upheld Sanader's conviction for taking bribes from Hungarian energy group MOL and an Austrian bank, but cut his sentence from 10 years to eight and a half years in prison.

Sanader had been found guilty in 2012 of having taken a five-million-euro ($6.7 million) bribe from MOL in order to secure  the Hungarian energy group's control of Croatia's state-run oil and gas firm INA.

In another case last year, Sanader was sentenced to nine years in jail after he was found guilty of embezzling millions of euros in public funds while in power.

Sanader has also been charged with abuse of power and corruption in several more cases, including over a building sale in 2009 and the sale of electricity from Croatia's utility to a Bosnian company at lower than market prices.

Sanader headed two conservative governments from 2003 to 2009 as leader of the HDZ party.

During that time he helped guide the former Yugoslav republic to NATO membership in 2009, and the country became the 28th member of the European Union in 2013 after launching a fight against corruption.