VIENNA (Reuters) - The number 2 figure in Austria s ruling Social Democratic Party has said he is resigning over a smear campaign against the main conservative party s leader, adding to a sense of disarray on the centre-left of politics weeks before a parliamentary election. The Social Democrats had denied having any connection with two websites making unsubstantiated allegations against 31-year-old Foreign Minister Sebastian Kurz, who took over the conservative People s Party (OVP) in May. Since Kurz took up his post, his party has topped the opinion polls. But Austrian newspaper Die Presse and weekly magazine Profil reported on Saturday that a former adviser to the Social Democrats who was dismissed this summer was originally behind the sites and that they had been kept in operation. At a hastily convened news conference on Saturday, Georg Niedermuehlbichler, the Social Democrats  chairman and campaign manager, said that until recently he had been unaware of any connection with the websites. Although the party never paid for or commissioned the websites, he said, he had discovered that one member of his staff had been aware of work on them.  It is my duty as election campaign manager to ensure that such things do not happen. They happened. I will therefore assume the consequences as campaign manager and as party chairman,  he said. Niedermuehlbichler s resignation adds to the troubles of a party that is now competing with the far-right Freedom Party for second place in the polls, well behind Kurz s OVP, ahead of a parliamentary election on Oct. 15. The Social Democrats remain deeply divided over whether to consider forming coalitions with the Freedom Party, having recently lifted a self-imposed ban on working with them. The Social Democrats are also at loggerheads with the OVP, in a country where parties rarely have enough votes to govern alone. The Freedom Party said Niedermuehlbichler s resignation was not enough and that the party leader, Christian Kern, should also step down.  Niedermuehlbichler appeared to blame Tal Silberstein, an Israeli political adviser who worked for the party until recently, for the websites. Profil and Die Presse also reported that he was originally behind them. The Social Democrats dismissed Silberstein in August after he was detained and questioned in Israel along with billionaire businessman Benny Steinmetz in a fraud investigation.  The events after that showed that this decision was right in every aspect, if too late. Evidently there were then activities that I could not imagine happening to that extent,  Niedermuehlbichler said.  It was certainly a big mistake to hire Tal Silberstein,  he added. Shortly before Niedermuehlbichler s announcement, tabloid daily Oesterreich published an interview with Silberstein in which it said he had declined to comment on the allegations about a smear campaign but said the party was right to sack him. On Saturday, Israel was observing Yom Kippur, when the country effectively shuts down for a day. 