Hundreds of thousands of people poured onto the streets of central Paris on Sunday to protest against President Francois Hollande's plan to legalize gay marriage and adoption by June.
Television footage showed some scuffles breaking out, with security forces firing tear gas on pink-clad marchers waving flags and chanting slogans against Hollande. In France, anti-gay protesters often wear pink.
Official police estimates put the turnout at around 300,000.
It was the second such protest this year after a similar march in January highlighted eroding public support for the bill that had forced deputies to put off a plan to allow lesbian couples access to artificial insemination.
President Hollande has pledged to push through the law with his Socialists' parliamentary majority and has angered opponents by trying to avoid public debate on the reform, which Justice Minister Christine Taubira described as a "change of civilization".
The French Senate is due to examine the bill in April.
Opponents of gay marriage and adoption, including most faith leaders in France, have argued that the reform would create psychological and social problems for children, which they believe should trump the desire for equal rights for gay adults.
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