Slovakian Prime Minister Eduard Heger (Photo: GI)

Only 27.3% of voters cast ballots, far below the absolute majority a referendum must attract to be valid, according to data released overnight by the Statistics Office.

Only one popular vote - on joining the European Union - has passed the threshold since Slovakia's independence in 1993.

An early election can be held in Slovakia if the constitution is changed to permit parliament's four-year term to be shortened. Such a change of constitution would need approval by a referendum or by at least 90 votes in the 150-seat parliament.

The government of Prime Minister Eduard Heger has been ruling in a caretaking capacity after it lost a no-confidence vote in parliament in December.