French President Francois Hollande on Thursday hit out at "homophobic" acts by opponents of a same-sex marriage bill following violent protests that included an overnight attack on a gay bar.

The interior minister, meanwhile, asked protest organisers to throw out members of far-right organisations who have been involved in the violence, as opposition intensifies ahead of the bill's expected final approval.

"Homophobic acts, violent acts have been committed. The right to protest is recognised by our constitution and accepted by the French. But no protest must degenerate," Hollande said.

The landmark bill was approved by the upper house Senate last week after being voted through the lower house National Assembly earlier this year.

It has now gone back to the assembly for a second reading, and could face a final vote as early as Tuesday, under a fast-track measure that has limited debate to 25 hours.

Opponents have accused the government of rushing the bill through its final stages in the legislative process, and have upped the ante with daily protests.

On Wednesday, a several-thousand-strong protest in the streets of Paris turned ugly with cars and public property vandalised and police officers and journalists attacked. Several people were detained for questioning.

In Lille, three employees of a gay bar were injured late Wednesday in an attack by four men who smashed the building's windows. The owner linked the incident to "tensions" over the parliament vote.

Protests against the bill -- which would also legalise same-sex adoption -- have also taken place in Versailles near Paris, as well as the southwestern city of Toulouse.

Interior Minister Manuel Valls denounced the current climate in France as "sickening" after holding a meeting with police representatives to reinforce security measures surrounding protests and try and prevent homophobic assaults.

He warned protest organisers to beware of "hate speech" and asked them to "reject far-right groups."

Meanwhile, debate in the lower house turned sour as pro- and anti-bill politicians traded barbs, with Justice Minister Christiane Taubira comparing the situation to "a bad Spaghetti Western" while one member of parliament said the proposed law equated to "assassinating children".

"What you are doing is (opening) a breach that will not close if this legal text passes through, it's an ignominy," said Philippe Cochet, member of the main opposition centre-right UMP party.

"You are assassinating children", he added, provoking an uproar that forced the speaker of the house to interrupt the session.

When the members of parliament returned, Cochet said the term he used was "not appropriate", but added he still believed the bill would make children more vulnerable.