Sitting on the floor, wearing traditional Islamic clothes and holding an old notebook, Abu Hamizi, 22, spends at least six hours a day searching internet chatrooms linked to gay websites. He is not looking for new friends, but for victims.

"It is the easiest way to find those people who are destroying Islam and who want to dirty the reputation we took centuries to build up," he said. When he finds them, Hamizi arranges for them to be attacked and sometimes killed.

The deputy leader of the group, which is based in Baghdad, explained its campaign using a stream of homophobic invective. "Animals deserve more pity than the dirty people who practise such sexual depraved acts," he told the Observer. "We make sure they know why they are being held and give them the chance to ask God's forgiveness before they are killed."