"Croatian Prime Minister Ivo Sanader unexpectedly announced his resignation Wednesday, saying he was withdrawing from politics," the German dpa news agency said adding that Sanader said he would propose deputy premier Jadranka Kosor as his successor.
The France Presse said that Sanader resigned two years before the expiry of his second term in office.
According to Reuters, local media earlier speculated Sanader would step down as prime minister to run for president in early 2010.
The Associated Press said that the local media had announced on Wednesday morning that Sanader was going to tender his resignation later in the day, and that nobody gave reasons for this move.