A leading international watchdog on Wednesday accused the militant Hamas group of abducting, torturing and killing Palestinians during the war in the Gaza Strip last year, saying some of the actions amount to war crimes.

Amnesty International detailed the abuses in a report entitled "'Strangling Necks': Abduction, torture and summary killings of Palestinians by Hamas forces during the 2014 Gaza/Israel conflict."

According to the London-based human rights group, some 23 Palestinians were shot and killed and dozens more were arrested and tortured by Hamas, which rules Gaza. The Palestinians targeted were either political rivals of Hamas, including members of the Fatah party of Palestinian President Mahmoud Abbas, or people the militant group had accused of co-operating with Israel, Amnesty said.

Wednesday's report highlighted a particularly brutal incident, which it said took place in Gaza on Aug. 22.

"In one of the most shocking incidents, six men were publicly executed by Hamas forces outside al-Omari mosque ... in front of hundreds of spectators, including children," Amnesty said. Hamas had announced the men were suspected "collaborators" who had been sentenced to death in "revolutionary courts," the rights group added.

"The hooded men were dragged along the floor to kneel by a wall facing the crowd, then each man was shot in the head individually before being sprayed with bullets fired from an AK-47," the report said of the August incident.

Hamas violently seized Gaza from forces loyal to Abbas in 2007, leaving Palestinians bitterly divided — Hamas ruling Gaza and Abbas governing parts of the West Bank. Since then, Hamas has launched thousands of rockets at Israel and fought three wars with it. Over 2,200 Palestinians were killed during the 50-day war last summer. On the Israeli side, 67 soldiers and six civilians were killed.

Hamas used the war to "ruthlessly settle scores, carrying out a series of unlawful killings and other grave abuses," Amnesty's Philip Luther said. "These spine-chilling actions, some of which amount to war crimes, were designed to exact revenge and spread fear across the Gaza Strip."

The report said 16 of the people killed by Hamas were already being held by the militant group when the conflict erupted and many of them were waiting to hear the verdict of their Hamas-organized trials. "Many had been sentenced after trials before courts whose proceedings are grossly unfair. A number had said they had been tortured in order to extract `confessions,"' the report said.

Amnesty's report also said that Hamas abducted and tortured people in an outpatient clinic that was no longer in use, within the grounds of Gaza City's main hospital, Shifa.

"Hamas forces have displayed a disregard for the most fundamental rules of international humanitarian law," Luther said. "Torture and cruel treatment of detainees in an armed conflict is a war crime. Extrajudicial executions are also war crimes."

This was not Amnesty's first report on the 2014 Gaza war.

In March, the group accused Hamas of war crimes for launching unguided rockets and mortars from civilian areas in Gaza toward civilian areas in Israel, saying that was a breach of international law. And in December, Amnesty condemned Israel for flattening four landmark buildings in the final days of the war. Israel dismissed that report, saying Hamas was using the buildings as command centres.

Salah Bardawil, a Hamas official in Gaza, said the incidents mentioned in the report took place "outside the framework of the law" and Hamas was investigating them.