Amnesty International said on Tuesday Hamas fighters in the Gaza Strip had carried out killings, torture and abductions of people accused of helping Israel, during and after the recent Israeli offensive. At least two dozen men have been shot dead by Hamas gunmen and scores of others have been shot in the legs, knee-capped or injured in other ways intended to cause permanent disability, the human rights group said.
Others have been severely beaten, tortured or ill-treated, it said in a report.
Most were abducted from their homes and later dumped, dead or injured, in isolated areas, or found in the morgue of one of Gaza's hospitals. Some were shot dead in hospitals where they were receiving treatment for injuries, Amnesty said.
The abuses have taken place since the end of December 2008, during and after the 22-day Israeli military offensive which killed some 1,300 Palestinians, the rights group said.
Amnesty International called on Hamas, the Islamist group which runs the Gaza Strip, to end the alleged campaign immediately and to agree to the establishment of an independent national commission of experts to investigate them.
"It's not clear whether this was something that was ordered or the top leadership effectively losing control of the guys with the guns," said Donatella Rovera, an Amnesty researcher who wrote the report.
Asked for comment on the report, Hamas spokesman Fawzi Barhoum said that, during the war, Israel deployed many informants to work against Hamas fighters and provided information that led to the killing of armed activists.
Hinting that some of those suspected of helping Israel were killed, he said: "There were also family feuds and people settling scores. Therefore, it is unjust to hold Hamas accountable for what happened."
"The government of national unity (Hamas) had the duty to implement the law and the resistance factions had the right to protect themselves," he said.
The targets of the campaign by Hamas forces and militias include former detainees, accused of helping Israeli security forces, who escaped from Gaza's Central Prison when it was bombed by Israel on Dec. 28, Amnesty said.
Others were former members of the Palestinian Authority security forces and other activists of Palestinian President Mahmoud Abbas's Fatah party, a rival to Hamas, it said.
Hamas, which won a Palestinian parliamentary election in 2006, routed Fatah forces in Gaza to take over the territory a year later.
An Amnesty International fact-finding team which visited Gaza during and after the Israeli offensive recorded testimonies from a number of victims, as well as medical sources and eyewitnesses who corroborated their stories.
Scores of others were too afraid to speak publicly for fear of retribution by Hamas forces or militias, the group said.
Among cases investigated by Amnesty, it said three brothers from the Abu 'Ashbiyeh family, from Jabalia in northern Gaza, were killed within 24 hours of escaping from Gaza's Central Prison in December.
Another former detainee at the prison, Jamal al-Ghandour, aged in his mid-50s, was shot dead in his bed in al-Shifa hospital on Dec. 28 by unmasked gunmen wearing plain clothes in front of relatives and other witnesses, it said.
Amnesty sought a meeting with Hamas to discuss the allegations but it was cancelled at the last minute, a spokeswoman for the group said. It would try to follow up on the report with Hamas, she said.