As Israeli police mounted a manhunt for the alleged failed British suicide bomber Omar Khan Sharif, fearing he would attempt another attack, human rights sources told the Guardian that Sharif and his accomplice Asif Mohammed Hanif, arrived at the offices of the International Solidarity Movement in Rafah and made contact with its members just days before the bombing.

The contact with the ISM, which has organised human shields and peace protests, could prove vital to the Israeli security services as they try to piece together the movements of the pair following their entry to the country.

One activist, who asked not to be named, recognised the pair when they were shown on Israeli TV. He spoke to them last Friday at the spot where American human shield Rachel Corrie was killed by an Israeli bulldozer. He said: "They did not seem tense or edgy. You didn't get the impression they were planning to carry out a suicide bombing within a few days.

"They were of Asian descent but they were very British. As soon as I heard their names on the television my heart sank. I didn't need to see the pictures. When they showed their passports on the TV, it was them."

The London office of the ISM was horrified by the contact with its sister office. John Heaney, a spokesman for the ISM, said: "I know for a fact they did not come through us in London.

"This is totally against what we believe in both as individuals and as a group. I've never met any kind of extremists out there among the peace protesters either with our group or any of the others we work with. My belief is that the whole movement is against violence."

At the same time British police were trying to uncover the lives of the two British Muslims allegedly involved in the bombing, who friends and family described as incapable of carrying out such an attack.

The men were unknown to the security services. Mr Sharif, 27, who apparently fought passers-by outside the Tel Aviv bar to escape after his belt containing explosives failed to explode, has two young children. The youngest of six children of Kashmiri immigrants, he attended a £12,000-a-year prep school.

Police in Derby confirmed that special branch officers and the Metropolitan police's SO13 anti-terrorist squad were investigating in the Normanton area of the city. A special branch officer said that Derby was "not especially a hotbed of Islamic radicalism".

Mr Sharif's accomplice, Asif Mohammed Hanif, 21, from Hounslow, west London, who died when his device detonated killing three people, was called "huggy bear" by his friends. Hanif, a former business studies student, was said to have shunned radicals who leafleted his mosque in west London.

His three other brothers and parents were yesterday struggling to come to terms with the reports of his death.

Israeli police say they recovered British passports belonging to the men. The Foreign Office said it could not rule out that they were fakes. Wednesday's attack, claimed jointly by Hamas and the al-Aqsa Martyrs' Brigade, was the first suicide bombing by a non-Palestinian in 31 months of fighting.