GAZA (Reuters) - Hamas security forces killed at least 32 Palestinian political rivals and suspected collaborators with Israel during and after the Israeli offensive in the Gaza Strip, Human Rights Watch said in a new report.

The report by the New York-based group said “unlawful arrests, torture and killings in detention” were making a mockery of Hamas’s claims to uphold the law in the Gaza Strip, territory ruled by the Islamist movement.

“Hamas should end its attacks on political opponents and suspected collaborators in Gaza which have killed at least 32 Palestinians and maimed several dozen more during and since the recent Israeli military offensive,” the report said.

Human Rights Watch said gunmen believed to be from Hamas tracked down and killed 18 Palestinians, most of them suspected collaborators, who escaped from Gaza’s main prison after Israeli aircraft bombed the facility on December 28.

The group said another 14 Palestinians, at least four of them detainees, had been killed by alleged members of Hamas security forces since Israel ended its 22-day offensive on January 18.

Taher al-Nono, spokesman of the Hamas government in Gaza, denied Hamas security forces were involved in extra-judicial killings.

He said “some resistance factions claimed they had killed suspected collaborators during the Israeli war on Gaza and in areas where battles took place, and we have launched an investigation which has not yet been completed”.

Nono said after the Israeli operation, 11 Gaza policemen were dismissed and could face criminal charges over their alleged involvement in the mistreatment of a detainee who was held on suspicion of drug dealing.

Human Rights Watch said it based its report on interviews with victims and witnesses in the Gaza Strip and on case reports by Palestinian human rights groups.

It said Palestinian authorities in the occupied West Bank, where Hamas’s main rival, the Fatah movement, holds sway have increased repressive measures against Hamas members and supporters.

Last month, a Palestinian group, the Independent Commission for Human Rights (ICHGR), said security forces controlled by Hamas in the Gaza Strip and those loyal to Fatah in the West Bank routinely carry out politically motivated arrests.

The ICHR said it had documented torture in Palestinian prisons in the two territories that included beatings, the removal of fingernails and sleep deprivation.

Hamas, which won a Palestinian parliamentary election in 2006, wrested control of the Gaza Strip from Fatah forces in 2007. Each side has accused the other of human rights abuses.