He also criticised Alvaro Uribe, the president, for not defending the initiative more forcefully.

"He said he supported the bill during his presidential campaign, but since then he's been silent," Benedetti said.

Vote

Slightly different versions of the bill had been approved by the senate and house of representatives and Tuesday's vote on the final version was expected to be routine.

"This was clearly a trick to sink the bill"

Marcela Sanchez, head of Colombia Diversa gay rights group
But a senator from a small party closely linked to an evangelical church called for a floor vote on the bill. Conservative politicians broke ranks with the pro-Uribe faction and it was defeated by 34 votes to 29.

"This was clearly a trick to sink the bill," Marcela Sanchez, head of Colombia Diversa, a gay rights group, said. "Never has a project reconciled by both chambers been called to a floor vote."

The bill would have granted same-sex couples living together for more than two years the same social security and estate inheritance guarantees as heterosexuals in common law marriages.

Although states and cities have passed similar laws allowing gay couples to share assets, no other country in the overwhelmingly Roman Catholic region has done so at a national level.