Amnesty International on Tuesday accused Hamas of waging a 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 have been shot dead by gunmen from the Palestinian militia that governs the Gaza Strip since December 27.
"Scores of others have been shot in the legs, knee-capped or inflicted with other injuries intended to cause severe disability, subjected to severe beatings ... or otherwise tortured or ill-treated," it added.
"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.
The victims included members of Palestinian Authority security forces and members of Palestinian President Mahmud Abbas' Fatah party, Amnesty said.
The campaign began shortly after the beginning of the three-week Israeli military offensive in the Gaza Strip on December 27 and continued after the ceasefire on January 18, according to Amnesty.
'Perpetrators did not conceal their weapons'
Palestinian human rights groups and victims first made such accusations at the end of last month, saying the Hamas rulers of Gaza were persecuting members of the rival Fatah movement to quash any opposition.
Taher al Nunu, a spokesman for Hamas, denied the charges at the time, dismissing them as "lies spread by Ramallah," where Abbas and the Palestinian Authority are based.
Amnesty International said the targets included former detainees who were accused by Hamas of collaboration with Israel after escaping from Gaza's central prison when it was bombed by Israeli forces on December 28.
Some were shot dead in hospitals where they were being treated for injuries suffered during the bombing raid, sometimes in front of distraught relatives, according to the testimony gathered by the human rights group.
"The perpetrators of these attacks did not conceal their weapons or keep a low profile, but, on the contrary, behaved in a carefree and confident - almost ostentatious - manner," the report noted.
Amnesty said there was "no doubt" that the victims were abducted, killed, shot and tortured by Hamas security forces and armed militias, adding that the evidence was "incontrovertible."
It called on the "Hamas de facto administration" to immediately end the campaign, accept an independent and impartial investigation and guarantee that victims and witnesses would not be targeted.