Amnesty International on Tuesday accused Hamas of waging a deliberate campaign to kill or maim scores of Palestinian opponents in the Gaza Strip since the end of December. The human rights group said in a report that at least two dozen men were shot dead by gunmen since December 27, when Operation Cast Lead began. "Hamas forces and militias in the Gaza Strip have engaged 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," the report said. "Scores of others have been shot in the legs, kneecapped or inflicted with other injuries intended to cause severe disability, subjected to severe beatings... or otherwise tortured or ill-treated," it added. One man told Amnesty International delegates, "Four masked men came to my house on 31 December 2008 at about 4 p.m.; they were armed with Kalashnikovs. They took me behind my house; they did not say anything. They shot me in the back of my right knee and then shot my left leg three times. My relative tried to intervene but they threatened to shoot him too." Many 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. 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 were able to corroborate their stories. Scores of others were too afraid to speak publicly for fear of retribution by Hamas forces and militias. Amnesty International called on he Hamas administration in Gaza to immediately end the campaign of abuses and to agree to the establishment of an independent, impartial and nonpartisan national commission of experts to investigate them.