PARIS (AFP) - President Francois Hollande on Wednesday urged France to put a divisive debate behind it after parliament defied months of protests to approve a bill legalising same-sex marriages.

"Today more than ever the country must rally behind what is expected by many of our countrymen: jobs, recovery and confidence," Mr Hollande told journalists after a cabinet meeting.

He said he would sign the bill, approved in its final second reading by parliament on Tuesday, into law as soon as France's Constitutional Council rules on a challenge filed by right-wing lawmakers.

"In the meantime, I am looking and calling on everyone to seek calm, understanding and respect because everything must now be focused and dedicated to what is essential - our country's economic success and national unity."

The bill, which also legalises adoptions by gay couples, sparked widespread opposition and months of street protests that occasionally spilled over into violence.

Several thousand protesters took to the streets again after its approval on Tuesday, with police clashing with a hard core of violent opponents.

The clashes saw protesters throwing firecrackers, bottles and stones at police, who responded with tear gas and made 12 arrests.

Gay activists celebrated the vote as a major step forward in their battle for equality and social tolerance.

"This law takes no rights away from anyone, it only grants rights to others," said Mr Nicolas Gougain, a spokesman for the Inter-LGBT rights group.

"This is liberation after years of fighting for equality."

Opponents of gay marriage have demanded a referendum and are still hoping they can build up enough pressure to persuade Mr Hollande to step back from signing the bill. Another mass protest is already planned for May 26.

But he showed no sign of backing down.

"This reform is in line with the evolution of our society and I am sure that we will be proud of it in the days to come, because this is a step toward the modernisation of our country, toward more equality, more freedom," Mr Hollande said.

The main opposition right-wing UMP filed the constitutional challenge almost immediately after the bill was approved, denouncing a fast-track voting procedure and saying it represents such a fundamental change that more than a law is required.

"This is not over," ex-prime minister Jean-Pierre Raffarin of the UMP told I-Tele. "There is a strong possibility that the (Constitutional) Council will take this up."

The UMP has not made clear whether it would seek to repeal the law if it comes to power. French media have reported that some in the party believe that would not be legally possible.

The council has a month to make a ruling, but the government has expressed confidence that the challenge would be dismissed.

Hundreds of thousands took to the streets in a series of protests against the bill, surprising many in a country that while predominantly Catholic is known for its secular traditions.

The reform initially seemed to enjoy solid majority backing among French voters. But recent polls have suggested the opposition campaign has shifted opinion to the extent that the electorate is now fairly evenly split on both gay marriage and adoption.

France's INSEE statistics agency says about 200,000 people declared themselves as living in same-sex couples in a 2011 study.

If Mr Hollande signs the law, France will become the 14th country to legalise same-sex marriages and join a club of eight other European nations - the Netherlands, Belgium, Spain, Norway, Sweden, Portugal, Iceland and Denmark.