SAN FRANCISCO (AFP) — Opponents of same-sex marriage in the US state of California, who won a referendum blocking the unions last month, said Friday they filed suit to annul thousands of gay marriages conducted in the state this year.Californians in a November 4 referendum on "Proposition 8" voted 52.1 percent in favor of a state constitutional amendment banning gay marriage, which the state Supreme Court had ruled permissible in June allowing some 18,000 gay couples to wed.Referendum proponents known as the "Protect Marriage" coalition on Friday took their campaign one step further, petitioning the Supreme Court to annul the gay marriages officiated so far in California."Proposition 8's brevity is matched by its clarity," the group said in its legal brief. "There are no conditional clauses, exceptions, exemptions, or exclusions: 'Only marriage between a man and a woman is valid or recognized in California.'"