Hamas gunmen used last month’s conflict in Gaza to murder, kneecap and torture Palestinian political opponents suspected of collaborating with Israel, Amnesty International has reported.

The human rights organisation said they had learnt of at least two dozen cases during Operation Cast Lead in which men were abducted from their homes and later dumped with horrific injuries or found dead in hospitals.

Among the incidents being investigated by Amnesty are the killings of three brothers who escaped from Gaza’s central prison, the murder of an al-Aqsa Martyrs’ Brigade commander who was shot in the head, and the torturing to death of a 51-year-old man by Hamas’ internal security forces.

An Amnesty spokesman said: “There is incontrovertible evidence that Hamas security forces and armed militias have been responsible for grave human rights abuses.

“The victims of such abuses and many others are being intimidated and discouraged from testifying about their ordeal.

“The Hamas de-facto administration has displayed a flagrant disregard for the most fundamental human rights norms, not only allowing such abuses to be perpetrated, but actually facilitating and encouraging them.”

He said Hamas spokesman Tahar al-Nunu, who pulled out of an arranged meeting with Amnesty staff last week, had later told a press conference: “There will be no mercy for the collaborators who have stabbed our people in the back.”

Amnesty called on Hamas to end the attacks and agree to the establishment of an independent, non-partisan commission to hold to account militiamen who committed the abuses.