Human rights violations in both the Gaza Strip and the West Bank have become widespread since fighting in June between the Palestinian factions saw Hamas seize control of Gaza, Amnesty International said on Wednesday.
Islamist Hamas and its secular rival Fatah each claims to represent the Palestinian national struggle, but their violent schism was widely seen as an unprecedented setback to hopes for a state in lands occupied by Israel in the 1967 Middle East war.
In a 57-page report, Amnesty International noted that the June civil war in Gaza in which some 160 people were killed had led to the creation, effectively, of separate Palestinian administrations in the Gaza Strip and the West Bank where political opponents have routinely been subject to abuse.
"Arbitrary detentions and torture or other ill treatment of detainees by Hamas forces are now widespread and the initial improvements in the security situation which followed Hamas' takeover are fast being eroded," the London-based group said.
Amnesty further criticised Hamas for entrusting its gunmen, who were trained to fight Israel and led the bloody rout of Fatah forces from Gaza, with law-enforcement duties.
"It appears clear that perpetrators of human rights abuses continue to enjoy impunity," the group said.
Amnesty also accused Palestinian President Mahmoud Abbas's Fatah of abuses in the larger West Bank, where it retains control and has conducted round-ups of Hamas sympathisers.
"Arbitrary detention of suspected Hamas supporters by Palestinian Authority security forces has become routine," it said.
According to Amnesty, Hamas and Fatah have each detained around 1,000 people since the June fighting, sometimes for periods of up to two weeks.
Torture of detainees has been commonplace, the rights group said citing victim testimony.
Hamas called the report unfair, saying its forces had acted to rein in lawlessness in Gaza while Fatah was conducting punitive actions in the West Bank.
"There has been a constant improvement in the security of citizens in Gaza," Hamas official Sami Abu Zuhri said, adding that any of the faction's fighters who acted unlawfully were "subject to constant monitoring and accountability".
Abbas's administration similarly shifted blame to Hamas while vowing a crackdown on abuses by Fatah fighters.
"There is a huge difference between an outlawed force committing human rights violations and legitimate security forces empowered by law," said Mahmoud al-Habbash, Palestinian minister for social affairs. "Mistakes may happen but we are doing our best."