"Palestinian armed groups made clear in their statements that harming civilians was their aim. There is simply no legal justification for launching rockets at populated areas," Sarah Leah Whitson, the group's Middle East director said in the report published Monday.
"A limited military arsenal that relies on largely indiscriminate rockets does not justify a failure to respect the law of war, which apply to all sides in a conflict whatever their capabilities. As the ruling authority in Gaza, Hamas has an obligation to stop unlawful attacks and punish those responsible."
Human Rights Watch officials said they interviewed Israeli residents and witnesses in towns and villages that came under attack from rockets fired from Gaza during the Israelis' Operation Pillar of Defense last month.
Under humanitarian law or the laws of war, civilians and civilian structures may not be the subject of deliberate attack that doesn't discriminate between civilians and military targets, the Human Rights Watch report said. It noted that groups in Gaza repeatedly fired rockets from densely populated areas, near homes, businesses and a hotel, placing civilians in the vicinity at grave risk.
The Gaza groups responsible for the rocket firing include Hamas, Islamic Jihad and the Popular Resistance Committee, Human Rights Watch said.
Islamic Jihad and Hamas officials said some of the rockets they fired were supplied by Iran, the report said.
Supplying weaponry to a party to a conflict knowingly is likely to be used to commit war crimes constitutes aiding and abetting of war crimes, the Human Rights Watch report states.