Supporters of gay rights take part in the 12th Croatian Gay Parade in Zagreb on June 15, 2013. Croatia has never had a gay marriage, but conservative activists say they want to block the possibility, after the centre-left government said it was preparing a law that would enable gay couples to register as "life partners"

Thousands took part on Saturday in Zagreb's biggest Gay Pride march, a day after Croatia's parliament received a petition signed by one-fifth of the EU-bound country's voters seeking a referendum that could rule out same-sex marriage.

"We have to show that we love Croatia where we live, but it also has to show that it loves all its citizens," Marko Jurcic, one of the organisers told the rally at a downtown square after an hour-long march.

"This is the country for all of us!" he shouted repeating the motto of the Croatian capital's 12th Gay Pride Parade in which some 12,000 people, according to organisers, took part.

On Friday a conservative group handed over to the parliament a petition with more than 740,000 signatures, in a country of 4.2 million people, collected during a virulent two-week campaign.

Some 1,000 supporters of the Catholic Church-backed group, In the Name of the Family, marched through Zagreb before giving the petition to the lawmakers.

It calls for a referendum on whether to add to the constitution a definition of marriage as a "union of a woman and a man". Currently there is no specific definition of marriage in the constitution.

Croatia has never had a gay marriage, but conservative activists say they want to block the possibility, after the centre-left government said it was preparing a law that would enable gay couples to register as "life partners".

The parliament must now review the petition but it has no deadline to do so.

"For Marriage Equality" read a giant pink banner carried at the head of a column of the Gay Pride marchers, escorted by special police who were however less visible than in previous years.

Participants blew whistles, waved rainbow flags while some were dressed in T-shirts saying "Marriage = Marriage", and carried banners that read "We don't Tolerate Intolerance" or "Jesus also had Two Fathers."

"I can hardly wait for us to marry," Milena Zajovic, dressed like a groom, told AFP.

"We expect a law over the issue to be adopted by the end of the year," the 30-year-old journalist said hugging her partner dressed in a long white wedding gown.

Her partner, Karla Horvat Crnogaj, 33, assured that "Croatia is ready to recognise same-sex couples."

Aleksandar Kosutic, a 43-year-old businessman, came to support his gay friends as he believes that the issue of marriage is "not an issue of sexual orientation but rather of human rights."

Gay activists and human rights groups in Croatia, which is set to join the European Union on July 1, have criticised the referendum initiative as "homophobic" and called on the government to block the move.

The issue has split the country where almost 90 percent of the population is Roman Catholic and the Church plays an important role.