A report by Amnesty International UK says that Hamas committed abuses that amount to war crimes during last summer’s 50-day war with Israel.

The terror group was accused of using last summer’s conflict as a cover to execute 23 Palestinians.

According to the report, the killings were carried out to “settle scores” against opponents under the assumption they were “collaborators with Israel”.

The report also says Hamas arrested and tortured of dozens of others during the war, including members and supporters of political rival Fatah.

Many of those killed were already serving sentences, had ongoing court cases or were appealing against death sentences.

Amnesty’s Middle East and North Africa director, Philip Luther, said: “It is absolutely appalling that, while Israeli forces were inflicting massive death and destruction upon the people in Gaza, Hamas forces took the opportunity to ruthlessly settle scores, carrying out a series of unlawful killings and other grave abuses.

“In the chaos of the conflict, the de facto Hamas administration granted its security forces free rein to carry out horrific abuses, including against people in its custody.

“These spine-chilling actions, some of which amount to war crimes, were designed to exact revenge and spread fear across the Gaza Strip.”

Atta Najjar was one of those killed during the spate of executions, according to Amnesty.

He was a former police officer under the Palestinian Authority and had already been tried and sentenced on accusations of collaboration in 2009.

Despite his conviction, and the fact he was already in prison serving a 15-year jail sentence, Najjar was among those executed on 22 August.

One of his brothers told Amnesty: “There were marks of torture and bullet shots on his body.

“His arms and legs were broken, his body was as if you’d put it in a bag and smashed it. His body was riddled with about 30 bullets.

“He had slaughter marks around his neck, marks of knives. And from behind the head - there was no brain.

“Empty, it was difficult for us to carry him … He was heavy, like when you put meat in a bag; no bones. His bones were smashed. They broke him in the prison.”

Amnesty has called on the Palestinian authorities, including the de facto Hamas administration in Gaza, to ensure that the cases documented in their report are investigated.

A report by Amnesty in March found that rocket and mortar attacks by Palestinian militant groups during last summer's conflict in Gaza amounted to war crimes.