Fawzi Barhoum, a spokesman for the Palestinian political faction, said the HRW report neglected to mention the reasons behind the disorder in Gaza that allowed the abuses to occur, namely Israel's bombing of police stations and prisons.
"This report, with all its details, is inaccurate and hastily-released, it lacks information and harms the policies of Hamas movement in Gaza Strip," Barhoum told Al Jazeera.
"We always aim at enforcing the law and respecting freedoms."
The HRW report said that fighters believed to be affiliated with Hamas tracked down and executed 18 Palestinians, apparently suspected of being Israeli collaborators, who had escaped from Gaza's main prison after it was bombed on December 28.
Taher al-Nunu, a spokesman for Gaza's Hamas-run government, admitted that a number of Palestinian factions had carried out killings of people suspected of collaborating with Israel.
"The [Hamas] government has opened an investigation into these killings, but it is not yet completed," al-Nunu said.
He said 11 police officers had been dismissed after the Israeli war, and could face criminal charges for alleged involvement in the mistreatment of a detainee.
The reports said that members of the rival Fatah party were reportedly attacked by Hamas members or their affiliates during the three-week war.
Another 14 Palestinians - at least four of them being kept in detention - were killed by police in the three months after Israel's assault on Gaza, the report said.
"The widespread practice of maiming people by shooting them in the legs is of particular concern," the report said.
It said that 49 people had been shot in the legs, while 73 Palestinian men had their legs and arms broken during the course of the 22-day conflict.
Ayman Mohyeldin, Al Jazeera's correspondent in Gaza, said he had heard numerous accounts of human rights abuses by several Palestinian groups during, and immediately after, the war.
"Al Jazeera was hearing accounts from Palestinians ... of how many of their loved ones had been detained following the war, had been taken, had been tortured, and sometimes evidence - as cited in the report - of Palestinians being shot in the leg, sometimes being killed ... at the hands of so many of these organisations," he said.
West Bank abuses
Human Rights Watch says its report is based on witness reports and testimony from victims, as well as case reports from Palestinian human rights groups.
The international rights watchdog also said "repressive measures" have increased against Hamas members in the occupied West Bank, which is controlled by Mahmoud Abbas, the Fatah leader and Palestinian president.
"Western governments that support and finance the Fatah authorities in the West Bank have remained publicly silent about the arbitrary arrests and torture against Hamas members and others," Joe Stork, HRW's deputy director for the Middle East, said.
The HRW report said Palestinian rights groups in the West Bank recorded 31 complaints of torture by police, as well as the death of at least one person in custody, and the arbitrary detention of two journalists considered to be pro-Hamas.
The Fatah-run Palestinian Authority, however, says all its arrests are in accordance with the law, and says no political arrests have taken place.
Al Jazeera is not responsible for the content of external websites.