Speculations about future cooperation between the HDZ and the HDSSB arose from the Croatian national broadcaster's feature on Monday about the latest developments in the HDZ branch in the eastern city of Osijek.
Sisljagic labelled the feature in the HTV primetime news programme as tendentious.
"After everything that the HDZ has done and is doing to the Croatian state, to the Croatian people and to the HDSSB party, one must be insane to think about cooperation with the party which plundered Croatia, sold national values and has been mired in crime and corruption," Sisljagic told a news conference in Osijek.
He said that the HDSSB was a sufficiently strong party and "is not even thinking about any coalition, particularly with the HDZ".
"The war between Jadranka Kosor and Vladimir Seks is behind the reported infighting in the HDZ Osijek branch," HDSSB Main Committee chairman Dinko Buric said.
He believes that HDZ president Jadranka Kosor and Vladimir Seks, one of the HDZ vice-presidents, are waging a war about "who will have a higher public profile".