The BBC's correspondent in New York, Jane Hughes: "Investigators are still searching for the gunman"

A gunman lay in wait outside the home of 51-year-old Dr Barnett Slepian and killed him with a single shot fired from a high-powered rifle when he and his wife returned home from a synagogue.

Dr Slepian had been the target of anti-abortion protestors for more than a decade but he had always vowed not to be deterred by them.

The shooting bore striking similarities to attacks carried out over the last four years on four other doctors in the area, though none of them were killed.

Earlier this week abortion clinic workers in up state New York and southern Canada were warned to take extra care.

'Americans must stand together'

President Clinton has issued a statement saying the nation cannot tolerate violence directed at those providing a constitutionally-protected medical service.

"No matter where we stand on the issue of abortion, all Americans must stand together in condemning this tragic and brutal act," he said.

George Pataki: Calling for death penalty

New York Correspondent Jane Hughes says abortion is one of the most divisive issues in the United States and anti-abortion violence has been increasing this year, with a spate of acid attacks on clinics in Florida and the bombing of a clinic in Alabama.

Two other doctors have been murdered in the last five years but Dr Slepian is the first to be killed at his home.

The National Organisation of Women has described the latest murder as domestic terrorism and called for more resources to protect doctors who carry out abortions.

A spokeswoman said it signalled an escalation of violence.

New York's Governor, George Pataki, says the perpetrator should receive the death penalty.