BBC Ireland Correspondent Mark Devenport reports on fears of further violence

A group of renegade loyalists, calling itself the Red Hand Defenders, says its members murdered Brian Service, 35, who was shot dead as he walked home on Saturday.

In a joint statement, Mr Trimble and Mr Mallon warned against retaliation and said the murder would not derail the peace effort.

BBC Ireland Correspondent Mark Devonport: This group is opposed to Good Friday Agreement

"Once again the cowardly men of violence have stepped from the shadows and murdered a man in his prime of life.

"There must be no succour given to these murderers. We must not let their evil desire for sectarian slaughter materialise."

Mr Service, a van driver, was found with gunshot wounds to his head and back lying in a street after midnight on Saturday morning.

He died later in hospital.

The shooting occured in an area where Catholic and Protestant neighbours meet.

Call for peace

The attacks were claimed in a call to a newsroom in Northern Ireland using a recognised codeword.

Meanwhile, Mr Service's family made an emotional appeal for no retaliation for his murder.

Father Kenneth Brady: No excuses for retaliation

Parish priest Father Kenneth Brady said the victim's distraught parents David and Anne did not want anyone else to suffer.

"They wish that no one will find any excuse to retaliate because of what happened to Brian.

"They also wish that the peace talks work so no one else will suffer this pain," he said.

Disaffected loyalists

The murder prompted fears that random sectarian killings had returned to the streets of Belfast.

Republicans said the killing was timed to heighten tensions in the peace process.

They also suggested it may even have been planned to coincide with the passing of Saturday's target date for the setting up of an executive of ministers for the Northern Ireland Assembly.

The Red Hand Defenders - a group of disaffected loyalists who oppose the peace process - emerged during the Drumcree crisis this summer.

They claimed responsibility for the blast bomb attack that killed Catholic RUC officer Frankie O'Reilly during riots in Portadown.

The group also admitted responsibility for an attack on a bar in republican west Belfast an hour before Mr Service was shot.