French President Francois Hollande hit out at "homophobic" acts by opponents of a same-sex marriage bill following violent protests that included an attack on a gay bar.
Interior Minister Manuel Valls 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.
There were even scuffles inside parliament itself.
"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 -- which would also legalise adoption by gay couples -- was approved by the upper house, the Senate, last week after being voted through the lower house, the 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 next 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 and have increased the pressure 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 two journalists attacked. Several people were detained for questioning.
The journalists from France's parliamentary television channel were "violently tackled and their equipment destroyed", the broadcaster, LCP Assemblee Nationale, said in a statement, adding that it would file a complaint.
In the northern city of 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 parliamentary vote.
Politicians have also been targeted. Socialist lawmaker Sylviane Bulteau, who supports the bill, said she had received a letter containing threats to kidnap her and to blow her up.
Protests against the bill have also taken place in Versailles near Paris, as well as in the southwestern city of Toulouse.
Interior Minister Valls denounced the current climate as "sickening" after meeting police representatives to reinforce security measures surrounding protests and to try to prevent homophobic assaults.
He warned protest organisers to beware of "hate speech" and asked them to "reject far-right groups", ahead of a large demonstration against the bill planned for Sunday.
Jean-Francois Cope, the head of the opposition right-wing UMP party, condemned the homophobic acts but said Hollande, "by refusing to listen to French people's concerns", was partly to blame for "deep divisions" over the bill.
The Archbishop of Paris, Andre Vingt-Trois, a fierce opponent of the gay marriage bill, appealed on Thursday evening for an end to the violence.
Debate in the lower house turned sour as pro and anti-bill politicians traded barbs. Justice Minister Christiane Taubira likening the situation to "a bad Spaghetti Western".
There was uproar when one member of parliament said the proposed law equated to "killing children", though UMP member Philippe Cochet later acknowledged that his words were "not appropriate".
At one point some UMP deputies advanced on the government benches after some members took exception to what they later said was mocking behaviour from a member of Taubira's team, a civil servant.
There were reports of punches being thrown as ushers intervened to prevent the situation degenerating any further.
Late on Thursday in central Paris there were more scuffles with police following another march against gay marriage. Demonstrators blamed a small group of far-right activists.
A police source said they had arrested at least 70 people.