Islamist regime has killed dozens and tortured others as 'collaborators' with Israel in war's aftermath, Amnesty and Guardian sources say

New evidence has emerged revealing the extent of the crackdown by Hamas during and after Israel's war in Gaza last month.

Amnesty International said Hamas forces and militias were involved in a "campaign of abductions, deliberate and unlawful killings, torture and death threats against those they accuse of 'collaborating' with Israel, as well as opponents and critics". It said at least two dozen men had been shot by Hamas since the end of December and "scores of others" shot in the legs, kneecapped or beaten.Amnesty gave detailed accounts of some of the cases and said there was "incontrovertible evidence" that Hamas security forces and militia were "responsible for grave human rights abuses". Hamas officials have admitted hunting for suspected collaborators, but they have denied this campaign of attacks.

Hamas apparently fears it lost some of its control in Gaza during Israel's devastating three-week war and launched a new and violent crackdown to enforce its rule, targeting not only those suspected of giving information to the Israeli military but also escaped prisoners and all perceived internal opponents.

The new evidence corroborates witness accounts given to the Guardian, as well as an investigation by the Palestinian Centre for Human Rights, based in Gaza City, that found 32 people had been killed by the Palestinian security services and other gunmen in Gaza since the war began, and that dozens more were shot or beaten.

In an interview today, one Palestinian working for a civil society organisation described how he was forced to leave Gaza because of the growing intimidation and threats. Mowaffaq Alami, 36, worked for the One Voice organisation in Gaza promoting grassroots discussions about Israeli-Palestinian peace proposals.

After Hamas took full security control of Gaza in June 2007, its forces raided the group's office and seized computers and other equipment. One Voice later closed its office, but the staff went on working from home. Then Hamas ordered all civil society groups to obtain its permission to continue their work. One Voice refused and six months ago halted all its work in Gaza.

"People are afraid to live normal lives, to express their opinions freely," Alami said. "There is no freedom of speech, of movement, of travelling or having real healthcare. Hamas is raising George Bush's policy: those not with us are against us." One of his colleagues was forced to leave Gaza after receiving threats from Hamas.

The Palestinian Centre for Human Rights said Hamas had tightened its restrictions on civil society groups, ordering them to inform the Hamas authorities before receiving or distributing aid and obtain Hamas approval before starting new construction or development work.

Alami, who secured a rare permit to leave Gaza a week ago with his family to live in the West Bank, said there were frequently differences between orders given by local Hamas commanders on the ground and the more senior leadership within the movement. Other small extremist movements were also beginning to return to force again – one prominent cafe in Gaza City was bombed last week.

He said many Palestinians no longer felt affiliated to any political group, either Hamas or Fatah, its West Bank-based rival. "Politicians and the media think that there is a simple division between Gaza and the West Bank, between Hamas and Fatah ... The majority of the Palestinian people today are with none of them."