A leading member of Brighton's Muslim community has urged Ken Bigley's kidnappers to set him free.
Dr Abdujalil Sajid, the Imam of Brighton and Hove, also told Tony Blair he should do more to help secure the British hostage's release.
Dr Sajid spoke to the Prime Minister for 15 minutes before both men attended St Peter's Church in Brighton yesterday.
He said: "No school of Islam allows the targeting of civilians or killing innocents. Indiscriminate, senseless and target killing has no justification.
"We as British Muslims wish to do all we can to see him safely returned to his family."
Mr Blair and his wife Cherie attended the service along with rural affairs minister Alun Michael and Chief Whip Hilary Armstrong.
As Mr and Mrs Blair arrived, a protester shouted: "Iraq war is a scandal. Scandalous! Blair Out!"
Another female bystander shouted at the Prime Minister: "My hero. I love you. You're the boss."
The Bishop of Birmingham, the Right Reverend John Sentamu, delivered a sermon on the theme of hope for the world.
Mr Blair made no comment to waiting reporters as he entered the church with Mrs Blair who was wearing a beige two-piece suit.
During the service, the congregation prayed for the safe return of Mr Bigley, 62, who was kidnapped in Iraq 11 days ago while working as an engineer.
Dr Sajid, a chairman of the Muslim Council for Religious and Racial Harmony, told Mr Blair negotiations must be kept open with the terrorists and that force was not the answer.
He said: "I said if you do not talk to the kidnappers, there is not hope. You cannot threaten someone who is not afraid to die - they must be won over.
"The fact is there were no international hostages, or even terrorists, before British and US armed forces moved in Iraq.
"More troops will create more terror, more violence and more anti-American and anti-British feeling.
"Mr Blair told me he could not bring the troops back now. He listened to me but we agreed to disagree."
The Imam said he feared the kidnappers' actions could lead to a rise in anti-Muslim feeling.
He said: "There was a backlash after 9/11 and the fear is real again. But we must address the fear and show solidarity together, as the people in Madrid did after the train bombings in March."
Dr Sajid has put together a booklet, entitled Know Your Rights and Responsibilities, backed by the Muslim Council of Britain, which will be sent to households across the country.
It states: "Averting a terrorist attack is an Islamic imperative."
Dr Sajid said: "We need to work with the police and agencies and play an active role in society to prevent terrorism.
"Public vigilance and co-operation is vital for ensuring security for all.
"Muslims have to make double efforts to address misunderstanding through dialogue and honest conversation."
Last night Ken Bigley's brother Paul Bigley said he had received news which gave him cause for hope.
"I have received information this evening that Ken is alive," he told a Labour Party conference fringe meeting via audio link.
Mr Bigley begged Tony Blair to help free his brother, saying his silence was "the kiss of death" for him.
He implored the Prime Minister to send a message to the Middle East media begging for him to be spared.
He said the Irish government had sent dozens of such requests but Downing Street had done nothing.
Speaking from the Netherlands to an anti-war meeting, Mr Bigley said he believed the Government was working behind the scenes to free his brother but Mr Blair was going about it the wrong way.
"All I am asking is for communication. Just simply send a bloody fax pleading for my brother's life."
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