Colleagues in the legal profession have also paid tribute to the work of Rosemary Nelson, who died after a car bomb attack at Lurgan, County Armagh.

Sinn Fein said it believed threats to her life had been made in the past.

Prime Minister Tony Blair called the attack a "disgusting act of barbarity" and expressed his sympathy for Ms Nelson's family.

Mr Blair met with Mrs Nelson in January as she represented residents in the Garvaghy Road area of Portadown affected by the continuing Drumcree dispute.

"The sole aim of the murderers is to remove any chance of reconciliation. They will not be allowed to succeed," said Mr Blair.

Northern Ireland's Deputy First Minister Seamus Mallon said he was "shocked and disgusted" at what he saw as "a mindless attack on peace".

Mrs Nelson represented the Garvaghy Road residents

Mr Mallon is one of many Northern Ireland political leaders in Washington for a St Patrick's Day meeting at the White House aimed at advancing the peace process.

In the province, the Alliance Party's chief whip, David Ford, said the murder was a "fundamental attack" on the human rights of everyone.

Tory leader William Hague condemned a "terrible and horrible crime" clearly designed to derail the peace process.

"I hope the people in Northern Ireland will have the resolve to continue with their work," he said.

Meanwhile, two MPs who jointly preside over the cross-party New Dialogue peace group, condemned the murderers as "fascist" and appealed for no retaliation.

"Those who carried out this monstrous attack must be hunted down with the utmost rigour by the RUC," said Labour's Harry Barnes and former Conservative minister Peter Bottomley.

The president of the Law Society of Northern Ireland, Katherine Dixon expressed her shock..

"Solicitors have worked over the many years of the troubles to provide the best possible service to the entire community," she said.

"It is extremely regrettable and of immense concern that a solicitor should be the victim of such an attack."

An emergency meeting of the Council of the Society has been called to consider the attack.

Pat Vernon, a solicitor who works for Mrs Nelson's practice, said: "I'm absolutely devastated. I'm disgusted any human being could do this to another."

He said Mrs Nelson had been a high-profile legal representative, but he had not been aware of any specific threat to her life.

Threat well known - Sinn Fein

However Sinn Fein's chief negotiator, Martin McGuinness MP, said it was "public knowledge that Mrs Nelson's life had been threatened".

He added that there had been a high-level security force presence in the area where she lived in recent days.

Some Lurgan residents are already blaming the police for Mrs Nelson's death, and held a demonstration after the bombing.

One man, who did not wished to be named said: "She was a lovely woman and was well respected in this community.