"Module No. 4 is unacceptable for Croatian pupils and it is inappropriate for the culture and world-view of the majority in the Croatian society," HDZ official Ante Corusic said in Zagreb at a news conference.

He reiterated that this opposition party was not against health education and that it was also for offering sex education as an optional class, just as religion.

Corusic compared the imposition of Module No. 4 to the "imposition of teaching Marxist ideology and the theory of self-managing socialism in Yugoslavia in the past".

The upbringing of children should be the parents' duty and not the duty of the state or (the party), he said alluding to the practice of the Communist Party during the Yugoslav era.

He called on parents not to allow their children to attend classes dedicated to Module 4 if they find the syllabus on sex education contrary to their world-view.

He also labelled Education Minister Zeljko Jovanovic as "an utterly irresponsible person, a party apparatchik" who earned degrees in education "only thanks to the authorities".

Corusic went on to say that the most frequently cited author in Module No. 4 is Theo Sandfort whom he described as an "active paedophile", who was deported from the Netherlands.

The HDZ official also criticised sexology as "a para-scientific discipline".

Later in the day, Minister Jovanovic said in response to the HDZ criticism that the health education curriculum was neutral and that health education "strengthens the family, and the society".

The four-module health education, which was introduced in Croatia's educational system last year, was abolished by the Constitutional Court towards the end of the 2012/2913 shool year due to procedural errors.

The education ministry reintroduced it this school year, claiming that the procedure was complied with this time.