Hamas conducted extrajudicial killings and kidnapped and tortured Palestinians the group believed were colluding with Israel during last summer's Gaza war, which left more than 2,000 Palestinians and 72 Israelis dead, Amnesty International has said.

The human rights group released a new report on Tuesday claiming that Hamas, the Islamist group that commands the Gaza Strip, routinely murdered and abused its rivals to "settle scores" during the conflict.

Many of the incidents were purportedly conducted as part of an operation codenamed "Strangling Necks," and were directed at those who allegedly had ties to or worked with Israel during the conflict. But Amnesty found Hamas had also summarily executed at least 16 people before the war began, according to the report.

"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," Amnesty's director of the Middle East and North Africa Program, Philip Luther, said in a statement. "These spine-chilling actions, some of which amount to war crimes, were designed to exact revenge and spread fear across the Gaza Strip."

Amnesty, which has previously documented the mass deaths and destruction committed by Israel, as well as by Hamas and other armed Palestinian groups, said atrocities and human rights violations were committed widely on both sides of the fence in 2014.

In a November 2014 report, the rights group said Israel's indiscriminate attacks on civilians during the Gaza offensive dubbed "Operation Protective Edge" amounted to "war crimes."

The latest Amnesty report also claims Hamas kidnapped and tortured other people it did not kill, including beating some supposed "collaborators" with gun butts, hoses, and wire, or holding them in stress positions.

Hamas reportedly also committed attacks against its main political rivals, Palestinian President Mahmoud Abbas's Fatah Party, in Gaza, which included some former members of the Palestinian Authority security forces.

"The Hamas leadership repeatedly calls for rights and justice for Palestinians in Gaza and elsewhere," said Luther. "But they do not always act in a manner that reflects respect for rights, justice and the rule of law."