Britain's top Muslims have branded the London suicide bombings "utterly criminal, totally reprehensible, and absolutely un-Islamic".
Muslims protest against terror at a rally in Leeds
A joint statement of condemnation came as 22 leaders and scholars met at the Islamic Cultural Centre, in London.
But Britain's highest ranking Asian police officer, Tarique Ghaffur, says Muslims and their leaders must do more than just condemn the bombings.
Bomber Hasib Mir Hussain's family said on Friday they were "devastated".
Police in Egypt arrested chemistry student Magdi Mahmoud al-Nashar, 33, wanted in connection with the bombings.
At the meeting in London, Muslim leaders said there could never be any excuse for taking an innocent life, it said.
Earlier, the head of the Muslim Council of Britain said he wanted "concrete steps" to make sure such atrocities were never repeated.
Sir Iqbal Sacranie, met Islamic and community leaders in Leeds, where three of the bombers were from.
The statement said everyone must confront the problems of Islamophobia, racism, unemployment, economic deprivation and social exclusion.
"Islam prohibits both anger and desperation. Anger and desperation are haram (forbidden) and may lead to some people being targeted by people with a sinister and violent agenda.
"There is, therefore, a great deal of positive work to be done with everyone in our own and wider community in order to channel the energy and talent of our youth, particularly into constructive avenues, serving God and society for the common good.
"The youth need understanding, not bashing."
Of the Muslim stance on suicide bombing, the leaders said: "There can never be any excuse for taking an innocent life.
"The Koran clearly declares that killing an innocent person was tantamount to killing all mankind and likewise saving a single life was as if one had saved the life of all mankind.
"This is both a principle and a command ... Those who carried out the bombing, the statement said: "Should in no sense be regarded as martyrs.
Both Muslims and non-Muslims should help bring the people behind the bombing to justice, it said.
"The pursuit of justice for the victims of last week's attacks is an obligation under the faith of Islam."
In his only interview on the attacks, Mr Ghaffur, the Metropolitan Police Assistant Commissioner, urged Muslims and their leaders to inform on potential terrorists and their supporters.
The police would protect informers, using the lessons learned from tackling serious and organised crime, the head of the Met's serious crimes directorate added.
They would have to engage better with minorities - but the minorities would have to take the first step, he said.
An air of radicalism had been building up among a minority of Muslims, Mr Ghaffur added.
But the London attacks had been the worst case scenario for Britain and its Muslims.
Earlier on Friday, Sir Iqbal Sacranie was reported to have met relatives of suicide bomber Mohammad Sidique Khan in Dewsbury.
He spoke to a number of groups in Leeds and said it was important to listen to the concerns of Muslims in the area.
"They are all in a state of shock, as we are," he said.
Sir Iqbal said that steps had to be taken within the UK's Muslim community.
He said: "The community across the country condemns such activities but beyond that, what have we been doing?"
His comments came as Met Police commissioner Sir Ian Blair met Muslim leaders and said police would work with the community.
Police have now turned their attention to finding those who may have helped the bombers carry out last Thursday's attacks - in which 55 people died, including three bombers.
They know three of the bombers were from West Yorkshire - Hussain, 18, of Holbeck, Leeds; Shehzad Tanweer, 22, of Beeston, Leeds, and Khan, 30, of Dewsbury - and are searching their homes.
They are also searching the home of the fourth bomber, Germaine Lindsay, a Jamaican-born man who lived in Aylesbury, Buckinghamshire.
British police are searching a house in Leeds linked to the Mr al-Nashar, but have not formally named him as a suspect in their investigation.
'Loving young man'
Mr al-Nashar denied having any role in the attacks and said he was on holiday, Egypt's Interior Ministry said.
He had told investigators all his belongings remained in the UK and he planned to return there, the ministry said.
The family of Hasib Hussain said in a statement their son was "a loving and normal young man who gave us no concern".
Prince Charles said the attacks had no link to "true faith"
"Our thoughts are with all the bereaved families and we have to live ourselves with the loss of our son in these difficult circumstances.
"We had no knowledge of his activities and had we done, we would have done everything in our power to stop him," the statement said.
In other developments Friday:
Forty-one bomb victims have been identified and 31 named.
The first funeral for one of the victims took place. Shahara Islam, 20, from Plaistow, east London, was buried at a private service.
The government plans new criminal offences of providing or receiving training in the use of hazardous substances; of acts preparatory to terrorism; and of inciting terrorism indirectly, Home Office minister Hazel Blears said.
It emerged bomber Mohammad Sadique Khan, a teacher, met MPs Hilary Benn and Jon Trickett during his school's trip to the Palace of Westminster in July 2004.
Victoria Line tube trains began to call at Kings Cross for the first time since the bombings.