Amnesty International said in a report on Wednesday that Gaza's dominant Islamist Hamas committed war crimes against Palestinian civilians in the territory alleged to have collaborated with the enemy during last year's war with Israel.
A ceasefire last August ended 50 days of fighting between Gaza militants and Israel in which health officials said more than 2,100 Palestinians, mostly civilians, were killed. Israel put the number of its dead at 67 soldiers and six civilians.
"Hamas forces carried out a brutal campaign of abductions, torture and unlawful killings against Palestinians accused of 'collaborating' with Israel and others during Israel's military offensive against Gaza," London-based Amnesty's report said.
A statement by Hamas denied involvement in the actions described by Amnesty, saying that rival Gaza families had taken part in "revenge attacks."
Earlier, a Hamas spokesman criticized the report as being unfair, unprofessional and not credible.
"The report is dedicated against Palestinian resistance (to Israel) and the Hamas movement ... It deliberately exaggerated its descriptions without listening to all sides and without making an effort to check the truthfulness of details and information," said Fawzi Barhoum, a Hamas spokesman.
In an earlier report in March, Amnesty criticized Israel and accused it of war crimes during the conflict. Israel said the report showed "extreme bias," had dismissed its security challenges and had ignored Hamas's actions.
Apart from the many deaths in the war, at least 16,245 homes were destroyed or rendered uninhabitable by Israeli shelling and air strikes. Gaza militants fired thousands of rockets and mortar bombs into Israel.
In Wednesday's report, Amnesty listed a number of cases it described as "spine-chilling" in which Palestinians accused by Hamas of helping Israel were tortured and killed.
"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," the Amnesty report said.
Hamas dominates the Gaza Strip, a densely populated desert enclave on the Mediterranean which borders Israel and Egypt.
The Palestinians joined the International Criminal Court after the war, a move opposed by Israel, and the ICC is now examining possible war crimes in the conflict. But joining the court also exposes Palestinians to possible prosecution if a case is opened.
(Writing by Ori Lewis; Editing by Mark Heinrich)