Maine has voted to repeal the state's recently passed gay marriage law.

With 87% of precincts reporting, 52.7% of votes were cast against gay marriage.

In May, state legislators passed a bill to allow same-sex marriage. Opponents -- backed by the Catholic church and the National Organization for Marriage -- quickly mobilized and forced a referendum on the issue.

Maine was seen as a key battleground for gay marriage in the US. The Maine vote came one year after California voted in favour of a similar measure -- Prop 8 -- which banned gay marriage in that state.

Gay marriage has lost in every state -- 31 in all -- in which it has been put to a popular vote.

However, in a Washington state referendum, early results suggest voters support a law that would expand domestic partnership rights for gays and lesbians. The state's new "everything but marriage" law has narrow approval so far, with a final result not expected until later this week.

Meanwhile, organizers of Maine's pro-gay marriage campaign vowed to continue the fight.

"We're in this for the long haul," says Jesse Connolly, No on 1 - Protect Maine Equality's campaign manager. "For next week, and next month, and next year -- until all Maine families are treated equally. Because in the end, this has always been about love and family and that will always be something worth fighting for."

National gay rights groups also expressed disappointment.

"This heartbreaking defeat in Maine unfortunately shows that lies and fear can still win at the ballot box," says Rea Carey, executive director of the National Gay and Lesbian Task Force. "Yet despite this setback, the tide clearly is turning nationwide in favor of marriage equality. We are confident that Maine will again join the growing number of states that extend the essential security and legal protections of marriage to all loving, committed couples."

Read more about the lead-up to the Nov 3 vote in our past coverage: Maine gearing up for gay marriage referendum in November.

Towleroad has a roundup of other races around the US, including Kalamazoo, Michigan's anti-discrimination measures.