Croatia's former prime minister Ivo Sanader was jailed Thursday after the Supreme Court increased his sentence to six years for taking more than €2 million in kickbacks while in power, state media reported.

Sanader, who led Croatia's government from 2003-2009, was handed a four-and-a-half year jail sentence in 2017 for pocketing the cash from a real estate deal.

On Thursday, police escorted the former premier to Remetinac prison after his jail term was increased to six years, Hina news agency reported.

"This is politically motivated persecution that has lasted for nine years and I will still fight by all means to prove my innocence," Sanader told reporters before being taken away.

According to the conviction, Sanader pushed his cabinet to buy a Zagreb building for the rural development ministry at twice its market value.

The government agreed to pay some 10 million euros for the property but €2.3 million were given directly to Sanader.

The 65-year-old has faced several other graft cases in which he is suspected of embezzling millions of euros.

In October he was sentenced to two and half years in jail for war profiteering, and acquitted of abuse of power charges in another trial.

Sanader, who helped guide Croatia to NATO membership, is the country's highest official to be charged with corruption since it declared independence from the former Yugoslavia in 1991.

Tackling graft was key for Croatia's successful bid to join the EU in 2013.