Žerjav made the surprise announcement in a letter to party members, which was circulated to the media late on Saturday, in which he expresses doubts about his ability to effectively lead the party and disappointment with the state of Slovenian politics.

The letter comes hot on the heels of a turbulent week for the SLS in which Maribor Mayor Franc Kangler, a leading member, was excluded from the party in the face of growing protests against him in Slovenia's second-largest city.

In a show of support to the embattled Kangler, the influential Maribor section of the SLS announced on Friday it would leave the party if Kangler's exclusion was not overturned.

In an indirect response to these threats, Žerjav said in the letter that he believed it was time to announce his decision to no longer lead the party.

While saying that he does not want to see members leave the party "because of me or the policies I have been promoting", Žerjav defended the decision of the SLS leadership to exclude Kangler following recent developments in Maribor.

Žerjav also expressed disillusionment with the state of Slovenian politics in general, saying it it "difficult to be part of a political class that is unable to make difficult decisions in such crucial times".

"It is hard being one of seven leaders of parliamentary parties who are unable to agree on anything. Not even on those issues for which there was consensus among us before the election. All because of a struggle for power."

Žerjav's announcement has surprised analysts and some of his fellow party leaders, while prompting a leading SLS figure to downplay its finality and its connection to any party disagreements.

SLS deputy group leader Mihael Prevc said in a response on Sunday that he hoped Žerjav's decision was not final. "There are still three months before the party congress."

Prevc also downplayed the importance of the recent developments involving Kangler for Žerjav's decision, arguing it was more a consequence of the ongoing blockade of reform efforts in the country.

The SLS does not appear to have a clear-cut successor to the 43-year-old Žerjav, whom it has promoted as its face ever since it elected him leader in 2009. In the December 2011 general election, the party's list was named "SLS - the List of Radovan Žerjav".

Emerging out of political obscurity in 2007, when he was appointed minister in the first Janez Janša government (2004-2008), Žerjav's popularity as a fresh face on the political scene capable of bridging the left-right divide has rubbed off on the SLS, which managed to turn around a steady decline in ratings witnessed in the decade before he took the helm.

While the 6% of the vote won in the December 2011 election was a far cry from the 19% the SLS won in the 1996 vote, it was the first time that the party had improved on its result from the previous election since hitting that peak.

Žerjav has also consistently polled among the most popular Slovenian politicians and as one of the most-liked ministers in the current centre-right government.