Hamas terrorists
Hamas terroristsMohammed Othman/Flash 90

Hamas used its 2014 Gaza war with Israel to "settle scores" with rival Palestinians, executing at least 23 in possible war crimes, Amnesty International said Tuesday, according to the AFP news agency.

A report by the London-based group detailed the "brutal campaign of abductions, torture and unlawful killings against Palestinians accused of 'collaborating' with Israel" by Hamas, de facto ruler of Gaza.

The report details the "extrajudicial execution of at least 23 Palestinians and the arrest and torture of dozens of others".

"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," Amnesty's Middle East and North Africa director Philip Luther was quoted as having said.

Hamas has a history of capturing alleged collaborators and executing them; at the very end of Operation Protective Edge, dozens of Gazans were rounded up and shot in a brutal killing spree.

The Palestinian Authority (PA)condemned the executions that were conducted without trial, amid speculation that Hamas was taking advantage of the situation to wipe out key members of its Fatah rival that is headed by PA Chairman Mahmoud Abbas.

The executions led Prime Minister Binyamin Netanyahu to famously compare Hamas with the Islamic State (ISIS) terrorist organization, telling the UN "ISIS is Hamas, Hamas is ISIS."

According to the new Amnesty report, "Hamas forces also abducted, tortured or attacked members and supporters of Fatah, their main rival political organization within Gaza, including former members of the Palestinian Authority security forces".

"Not a single person has been held accountable for the crimes committed by Hamas forces against Palestinians during the 2014 conflict, indicating that these crimes were either ordered or condoned by the authorities," it said.

Luther accused Hamas of "appalling crimes against powerless individuals", which in some cases constitute war crimes.

He said the movement displayed "a disregard for the most fundamental rules of international humanitarian law".

Amnesty called on the Ramallah-based Palestinian Authority and Hamas to "cooperate with independent and impartial international investigative mechanisms", and to bring "suspected perpetrators" to justice.

A March report by Amnesty found that rockets fired during Operation Protective Edge by Gaza terrorists killed more Palestinians than Israelis.

Hamas at the time rejected the report, claiming it “adopts the Israeli version” of the story.