MEXICO CITY - The Mexico City legislature voted Tuesday to legalise abortion, after several weeks of heated debate in which conservative groups and the Catholic Church traded insults with pro-choice activists and threatened them with excommunication.

Mexico City has now joined Cuba and Guyana as the only places in Latin America where abortion is legal.

The bill must now be signed into law by Mexico City Mayor Marcelo Ebrard of the leftwing Democratic Revolution Party (PRD), who said he would do so quickly. The new law will make abortion on demand legal in the city in the first 12 weeks of pregnancy.

Women's groups and the PRD, which has dominated the municipal government and the city legislature since 1997, said the new law was a triumph for the rights of women.

Meanwhile, the Catholic Church and conservative groups, which held marches and days of prayer against the bill, lashed out against the measure as an attack on life itself.

"The decriminalisation that has been approved is a disgrace, but we have not lost the battle," Jorge Serrano, head of the anti-abortion group Comité Pro Vida, told IPS.

"We will not recognise this law and we will go to the clinics and hospitals where abortions are practiced to denounce them and try to keep them from carrying them out," he warned.

During the debates in the city legislature, small anti-abortion and pro-choice groups demonstrated outside with placards, chants and music. The demonstrators were not allowed into the building, which was guarded by the police.

Conservative groups demanded that the issue be decided in a referendum, and presented 70,000 signatures to that end. However, the PRD refused to consider that possibility.

"The rights of women cannot be put to a vote," Lorena Martínez, a member of a university women's group, told IPS.

The numerous surveys on the question carried out by private polling firms and national newspapers show that a majority of people in the capital are in favour of legal abortion, although around 40 percent are opposed to it.

The decriminalisation of abortion in the city enjoys a high level of support despite the fact that an overwhelming majority of Mexicans profess Roman Catholicism, whose leaders excommunicate those who practice abortion.

The government of President Felipe Calderón of the conservative National Action Party (PAN) is opposed to the bill passed by the city legislature, but its spokespersons have said it will respect the new law.

Nevertheless, the PAN leadership announced that it would object to the decriminalisation before the Supreme Court.

Pope Benedict XVI also spoke out, drawing fire from the left, which complained that the Vatican was meddling in the affairs of another state.

The Calderón administration itself told the Church that it had gone too far, through the Interior Ministry's head of religious associations, Salvador Beltrán del Río.

In a letter dated Apr. 20, the Pope urged Roman Catholics in Mexico to oppose decriminalisation of abortion and to staunchly defend every human being's right to life, from the moment of conception, against any attack from the "culture of death."

Mexican Archbishop Felipe Aguirre warned that all those who aid and assist in an abortion will be automatically excommunicated.

The head of Pro Vida said that "whoever supports this criminal law will pay for it in the next elections. They will not escape punishment."

PRD members of the Mexico City legislature reported some days ago that they had received anonymous death threats by telephone and e-mail in recent weeks, because of their support for legalising abortion.

Representatives of the PRD explained that the goal of the new law is not to encourage abortion, but to recognize the reality and regulate it.

Mayor Ebrard said his administration does not encourage abortion, but pointed out that back street abortions frequently lead to injury and death.

The mayor said that his administration will support sex education and the use of contraceptive methods to avoid unwanted pregnancy.

Although abortion in Mexico is considered a crime -- with some exceptions -- which carries a penalty of between one and six years in prison, only 28 women who had an abortion between 2000 and 2006 were prosecuted, and 14 were sentenced, out of the estimated one million women who resort to it every year.

A study by the National Autonomous University of Mexico (UNAM) estimated that in this country of 104 million people, up to one million illegal abortions are carried out a year, equivalent to one-third of annual pregnancies. However, other sources quote a figure of less than 500,000 abortions a year.

Mexico's 32 states all permit termination of a pregnancy arising from rape, 27 states allow it when the mother's life is at risk, 13 if the fetus is seriously malformed, and 10 when the aim is to protect the mother's health.

Other studies show that unsafe illegal abortions are the fourth or fifth cause of death among women in Mexico, and that obtaining permission for a legal abortion in any of the abovementioned circumstances is difficult and often nearly impossible.

Of the 193 United Nations member countries, 188 allow therapeutic abortions, carried out for the wellbeing of the mother. Only Chile, El Salvador, Honduras, Nicaragua and the Vatican prohibit abortion under any circumstances, according to the World Health Organization (WHO).

In Latin America and the Caribbean, abortion is available on demand only in Cuba and Guyana, although in nearly every other country activists and women's organizations are clamoring for decriminalization before the fetus is viable, that is, capable of living outside the womb, which the WHO defines as before 20 weeks' gestation.

The WHO says that some four million abortions are practiced in the region every year, and that 5,000 women die from backstreet abortions. A further 30 to 40 percent of women who have abortions in those conditions suffer severe complications.