Mike Rounds, a Republican, signed a law on Monday that bans abortion in almost all cases, punishing doctors who perform one with five years in prison and a $5000 fine.

It bans abortion even in cases where a woman is pregnant as a result of rape or incest, or if giving birth would damage the health of the mother.

The only narrow exemption in the law applies to cases in which a doctor's effort to save a pregnant woman's life results in the accidental death or injury of her foetus.

Rounds acknowledged that his action would provoke a legal battle that could take years to resolve.

Anti-abortion activists will seek to use the South Dakota law to eventually bring the issue back to the Supreme Court.

Costly battle

They believe conservatives added to the bench by George Bush, the US president, and others who may join it in the future could weaken or dismantle the court's landmark Roe v Wade decision of 1973.

NARAL Pro-Choice America, which backs abortion rights, put an emergency appeal for money on its website, urging its supporters to help with what may prove to be a costly battle.

"President Bush has created a climate with his judicial appointments in which anti-choice lawmakers feel emboldened"

Nancy Keenan, president,
NARAL Pro Choice America

Nancy Keenan, the president of the group, said: "This law is a monumental setback for women in South Dakota and across the country. Anti-choice politicians in 11 other states are pushing similar bans.

"President Bush has created a climate with his judicial appointments in which anti-choice lawmakers feel emboldened."

David Bereit, executive director of the American Life League, called the South Dakota development "tremendously encouraging news".

No legal actions have yet been officially launched against the law.

Defiant stand

However, Planned Parenthood, which operates the sole abortion clinic in South Dakota where about 800 of the procedures are performed each year by doctors from neighbouring Minnesota, said it was preparing a challenge.

Kate Looby, state director for the group, said "all options are being considered at this time".

She said the governor "cares more about politics than about the reproductive freedom of women in South Dakota".

Looby said: "Our doors remain open. We will not be closing - hopefully never."

Troy Newman, head of the anti-abortion group Operation Rescue in Wichita, Kansas, said that abortion had never been been put before voters and pro-abortion groups could not win.

"The timing couldn't be better and reflects the momentum the pro-life movement has today," he said. "It's a grassroots movement that's propelling the legislatures, the governor, the president, and ultimately the Supreme Court to nullify the permissive abortion laws."

Even before Rounds signed the measure into law, backers in South Dakota said am anonymous donor had pledged $1 million to help the state fend off legal challenges to it.