SANTIAGO, Chile — Approval of a law legalizing abortion in some cases in Chile will have to wait after its supporters narrowly lost a lower house vote on proposed modifications to the bill.

Chile’s Senate on Wednesday voted to allow abortions when a mother’s life is in danger, when the fetus is not viable and in cases of rape. It was seen as a dramatic development in one of Latin America’s most traditionally conservative countries.

The lower house had already approved the bill, which was strongly backed by President Michele Bachelet, leading many to expect its passage into law.

But modifications made by the Senate were sent back to the lower house for approval where they failed to pass by just one vote. While abortion has met resistance from Chile’s conservative sectors, Thursday’s failure was due to the abstention of a member of Bachelet’s party.

“This is painful for us. Nobody tried to align everyone because it was understood that we were all committed to what we had promised the citizens,” said backer Sen. Alejandro Guillier.

Chile is one of just four countries that currently prohibit abortion in all cases, according to the New York-based Center for Reproductive Rights. A handful of others have rules so restrictive that they amount to de facto bans.

Currently women who get abortions in Chile are subject to up to five years in jail, as are doctors or medical personnel who assist with the procedure. A woman who arrives at a hospital with signs that she has had an abortion is supposed to be reported to the police, or the hospital faces sanction.