Slovakia's parliament on Thursday rejected a treaty safeguarding women for a second time and called on the country's populist government to block the European Union from adopting it.

Spearheaded by the Council of Europe, the treaty is the world's first binding instrument to prevent and combat violence against women, from marital rape to female genital mutilation.

Presented by the rights watchdog for ratification in 2011, the convention has been approved a majority of EU member states.

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Slovakia's parliament first rejected the treaty in March insisting, without proof, that it is at odds with the EU country's constitutional definition of marriage as a heterosexual union.

Nationalist lawmakers went a step further on Thursday, proposing a resolution that calls on the government to "prevent" the European Union from accepting the "scope of obligations" that arise from the Istanbul Convention that "are not provided for in the Slovak legal order".

Ninety-three representatives voted in favour of the resolution, 29 against and 13 abstained.

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Council of Europe Secretary General Marija Pejcinovic Buric called the move "a regrettable step backwards", according to an emailed statement.

"European governments should do more to end violence against women, not less," she added, calling on "responsible politicians at the national level" to "dispel misconceptions and misunderstandings about the convention."

While there is no explicit mention of gay marriage in the Istanbul Convention, many Slovaks view its wording as a threat to the traditional family structure.

A controversial 2014 constitutional amendment defines marriage in Slovakia as a union between man and woman.