RAMALLAH, West Bank — A West Bank journalist was detained by Palestinian Authority security forces for four days after he took photographs on his cellphone of the Palestinian prime minister’s convoy stuck in line at an Israeli-controlled checkpoint.

An activist in Gaza said that Hamas security forces detained him for 15 days after he wrote a Facebook post protesting the lack of electricity in which he asked the group’s leaders if their children slept on the tiled floor to escape the heat, as his did.

Citing those cases and others in a report published on Tuesday, Human Rights Watch, the New York-based advocacy organization, accused both the Western-backed Palestinian Authority and its rival, Hamas, the Islamist militant group that controls Gaza, of routinely using arbitrary arrest and torture as tools to crush dissent.

The systematic practice of torture by the two authorities might amount to a crime against humanity and could be prosecutable at the International Criminal Court in The Hague, the report said.