Amnesty International says it has evidence that Hamas forces and militias have been involved in a ruthless crackdown on opponents in the wake of the Israeli military action in the territory.
The leading human rights organisation talks of a "campaign of abductions, deliberate and unlawful killings, torture and death threats against those [Hamas] accuse of 'collaborating' with Israel, as well as opponents and critics".
It says that at least two dozen men had been shot by Hamas since the end of December 2008 and "scores of others" shot in the legs, kneecapped or beaten.
Amnesty has been given 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 continue to deny 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, says the Guardian newspaper, which has also looked at the evidence.
The Palestinian Centre for Human Rights, based in Gaza City, says 32 people had been killed by the Palestinian security services and other gunmen in Gaza after the war began, and dozens more were shot or beaten.
After Hamas took full security control of Gaza in June 2007, its forces raided another civil society group's offices and seized computers and equipment. 'One Voice' subsequently closed its office, but staff worked from home.
Hamas also 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.
The Palestinian Centre for Human Rights says Hamas has tightened its restrictions on civil society groups, ordering them to inform the authorities before receiving or distributing aid and obtain Hamas approval before starting new construction or development work.
One NGO worker said many Palestinians no longer felt affiliated to any political group, either Hamas or Fatah, its West Bank-based rival.
He told the Guardian: "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."
Human rights groups say that Israel may need to face war crimes charges for its actions in Gaza. But they also similarly accuse Gaza of attacks on civilians, though not on anything like the same scale.