Gunmen with suspected links to Hamas security forces in the Gaza Strip killed at least 32 Palestinians and wounded dozens in attacks on political opponents and alleged informers during and after Israel's recent war in the coastal territory, an international human rights group said Monday.

The New York-based Human Rights Watch urged Gaza's Hamas rulers to halt what it described as a pattern of arbitrary arrests, torture and summary executions by the Islamic militant group.

Human Rights Watch portrayed the attacks as the worst outbreak of internal violence since Hamas militants violently seized control of Gaza in June 2007 and expelled rivals in the more moderate Fatah movement of Palestinian President Mahmoud Abbas, who now controls only the West Bank.

Such practices are aimed, in part, at quashing dissent in Gaza and make a mockery of Hamas' claim it upholds the law, the group said.

During the war, "Hamas authorities ... took extraordinary steps to control, intimidate, punish and at times eliminate their internal political rivals as well as persons suspected of collaborating with Israel," the report said.

Eighteen Palestinians were killed by Hamas during the three-week war, which ended Jan. 18, and 14 others were killed afterward, the report said. In addition, 49 Gazans were shot in the legs by masked gunmen between Dec. 28 and Jan. 31, and 73 had their arms or legs broken, the report said, citing a rights group linked to Abbas.

Hamas spokesman Fawzi Barhoum dismissed the Human Rights Watch report as unbalanced. He said Hamas was willing to investigate any complaints, and denied the group is going after political opponents.

He said suspected collaborators with Israel who fled Gaza's central prison after it was destroyed in Israeli bombing raids in December were killed by relatives of people they had harmed, not by security forces.

Other international and Palestinian human rights organizations have provided similar accounts of shootings and beatings. Fatah has also said 14 of its members in Gaza were killed by Hamas during the Israeli offensive and that more than 160 were shot in the arms or legs or beaten.

Human Rights Watch said repressive measures are also on the rise in the Abbas-controlled West Bank.

Abbas' security forces have been cracking down on Hamas in the West Bank since the militants seized Gaza. Hamas detainees in West Bank prisons have complained of mistreatment, including beatings and being tied up in painful positions. In January and February, one detainee died in custody, and 31 complained of mistreatment, Human Rights Watch said.

The report about the Gaza abuses is based on interviews with witnesses and victims, as well as reports by Palestinian human rights groups, Human Rights Watch said.

It reviewed killings and shootings since Dec. 27, when Israel launched its Gaza offensive, meant to weaken Hamas and halt rocket attacks from Gaza on Israel.

Hamas has begun investigations into four deaths, dismissing and detaining members of the security forces involved in two killings, said Bill Van Esveld, a Human Rights Watch researcher.

"What we have not seen is accountability for (the killing of) collaborators and Fatah guys getting shot in the legs," he said.

In a recent case under investigation, gunmen wearing headbands of Hamas' military wing, Izzedine al-Qassam, reportedly opened fire Thursday on three cousins loyal to Abbas' Fatah movement in the Gaza town of Jebaliya.

The three men were each hit by several bullets in the legs and remain hospitalized, the Gaza-based Palestinian Center for Human Rights said.